Acceptance Testing Introduction and Basics

Fundamental Relationships

While it is certainly true that the roles and responsibilities of the tester and the business analyst are different, it is also true that their activities are complementary; work done by one group may greatly affect, either positively or negatively, that of the other. This is especially true in acceptance testing which is performed to assess the system’s readiness for deployment and its use by the customer (end-user). Good collaboration between business analysts and testers is particularly important for a proper consideration of the business implications at this test level.

Business Goals, Business Needs and Requirements

Business analysts first must understand the organisation’s overall business goals and identify current business processes and stakeholders. Once that is done, they describe specific business needs and determine a business case that addresses those needs. Once this high-level work has been completed, requirements can be elicited for the business solution that shall be developed.

Business goals, business needs, business requirements, and product requirements describe, at different levels of abstraction, what shall be achieved. In Agile development, the same principles apply, but different terms may be used (for example features and user stories).

In this document, the term “requirements” refers both to business requirements and to product requirements.

Requirements / User Stories, Acceptance Criteria and Acceptance Tests

During requirements elicitation, business analysts and testers (possibly together with developers) should begin to create specific acceptance criteria and develop acceptance tests as a joint effort. This ensures that there is a mutual understanding of what “acceptable” means from the business, development, and testing perspectives, right from the beginning of the project.

Acceptance criteria relate directly to a specific requirement or user story. They are either part of the detailed description or an attribute of the related requirement. If user stories are used, acceptance criteria are part of the user story’s definition and extend the story. 

In all cases, acceptance criteria are measurable criteria, formulated as a statement (or a set of statements), which can be either true or false. They are used to check whether a requirement or user story has been implemented as expected. Acceptance criteria represent the test conditions which determine “what” to test. They do not contain the detailed test procedures. 

Acceptance test cases are derived from acceptance criteria. These tests specify how the verification of the acceptance criteria should be performed. 

The Importance of the Quality of the Requirements

If acceptance criteria and tests are based on requirements, user stories, and/or acceptance criteria that are vague or ambiguous, it is likely that testers will make assumptions about stakeholder expectations and business needs. In this case, the resulting acceptance tests may be flawed. This will lead to rework or, even worse, the running of invalid tests, thus creating unnecessary costs as well as risks and uncertainty about product quality assurance. 

It is critical for testers to work closely with business analysts to make sure that requirements are clear and well understood by all stakeholders concerned. Ambiguities should be resolved and assumptions should be clarified so that the resulting acceptance tests are valid and are a meaningful way to determine the product’s readiness for release. 

In Agile development, the INVEST criteria define a set of criteria, or checklist, to assess the quality of a user story. These may be used by business analysts / product owners, developers, and testers to ensure the quality of user stories.

Business Analysis and Acceptance Testing

Too often, business analysts and testers work in their own separate silos, which can lead to misunderstandings about business and customer expectations. Those misunderstandings may stay hidden until the release approaches. By taking advantage of the complementary skills and by working together, business analysts and testers can positively affect the development process. This can be accomplished both by considering acceptance criteria and acceptance testing as early as possible and by coordinating efforts to make sure that the product has been tested appropriately prior to release at acceptance test level. 

Relationship between Business Analysis and Testing Activities

The following are the main elements of the business analysis activities: 

  • Strategy definition
  • Management of the business analysis processes
  • Requirements engineering in business analysis
  • Solution evaluation and optimisation

The business analyst is responsible for identifying business needs of stakeholders and for determining solutions to business problems with the aim of introducing change which adds value to the business. An important aspect of the business analyst’s role is to establish consensus between quality engineers, testers, developers, system integrators, product managers and project managers.

A test process consists of the following main groups of activities:

  • Test planning
  • Test monitoring and control
  • Test analysis
  • Test design
  • Test implementation
  • Test execution
  • Test completion

Quite a few of the associated activities and tasks relate to both business analysis and testing. The following examples illustrate the relationship between the two disciplines in the context of acceptance testing:

Requirements engineering in business analysis vs. test planning, test analysis and test design:

  • During the requirements engineering activities in business analysis, business analysts prepare detailed business and product requirements. These requirements are part of the test basis for the test planning, test analysis and test design activities, as testers define their objectives and plan their work, evaluate the specifications and requirements, identify test conditions and design test cases and test procedures.
  • Testers can contribute to the definition and verification of acceptance criteria as part of test analysis and test design activities. Working together, the two roles ascertain that there is proper understanding of the solution and agree on the appropriate approach to acceptance testing.
  • When requirements change, business analysts and testers can work together to assess the impact of the changes.

Solution evaluation in business analysis vs. test implementation, test execution and test completion:

  • During the solution evaluation phase in business analysis, business analysts support test implementation and test execution activities. They review the testers’ procedures/scripts, clarify issues and potentially help with creation of test data to support business-related tests.
  • Business analysts can assist with the implementation and execution of the acceptance tests. They may also support testers by evaluating test results. In addition, they may assist testers in test completion activities.

There is a strong and symbiotic relationship between the two roles and their respective activities, starting at the very beginning of a project and continuing until acceptance or release of the solution.

Collaboration between Business Analysts and Testers in Acceptance Testing

The common goal for business analysts and testers is to support the production of products with the highest possible value for the customer. Given their position within the organisation, business analysts and testers have various opportunities to collaborate during the acceptance testing activities described in the previous section. Apart from joint discussions and reviews of generated artefacts, business analysts and testers collaborate in other areas. For example, collaboration on test planning based on risk analysis is a good opportunity to ensure that the appropriate test cases will be developed and prioritised.

In addition to the direct benefits of working together and supporting each other’s efforts during acceptance testing, there is an important opportunity to cross-train team members. The more testers know about business needs and stakeholder requirements, and the more business analysts know about structured testing, the more likely the two groups will understand and appreciate each other’s work and better collaborate within the project.

How Acceptance Testing Can Drive the Development Process: ATDD and BDD

The wide acceptance of Agile software development practices has influenced how acceptance testing relates to requirements elicitation and other business analysis activities. In sequential lifecycle models, acceptance test analysis, design, and implementation are activities to be handled by the testers after the requirements are finalised. With the Agile lifecycle model, acceptance criteria and acceptance test cases are created during requirements analysis, requirements refinement sessions, and product backlog refinement. This allows the implementation of the “Early Testing” principle by using the design of test cases as part of the requirements definition activities. 

In the following two approaches, acceptance test analysis and design are formally part of the requirements engineering process: 

  • In Acceptance Test-Driven Development (ATDD), acceptance tests are produced collaboratively during requirements analysis by business analysts, product owners, testers and developers.
  • Behaviour-Driven Development (BDD) uses a domain-specific scripting language, Gherkin, that is based on natural language statements. The requirements are defined in a ‘Given – When – Then’ format. These requirements become the acceptance test cases and also serve as the basis for test automation.
  • Both of these approaches engage the entire Agile team and help to focus the development efforts on the business goals. The approaches also treat the acceptance test cases as living documentation of the product because they can be read and understood by business analysts and other stakeholders. Acceptance test cases represent scenarios of usage of the product.
  • The two approaches are similar and the two terms are sometimes used interchangeably. In practice, BDD is associated with the use of Gherkin to support writing acceptance tests, while ATDD relies on different forms of textual or graphic acceptance test design. For example, the graphical representation of application workflows may be used to implement a visual ATDD approach.

Testing Throughout the Software Development Lifecycle

Software Development Lifecycle Models

A software development lifecycle model describes the types of activity performed at each stage in a software development project, and how the activities relate to one another logically and chronologically. There are a number of different software development lifecycle models, each of which requires different approaches to testing.

Software Development and Software Testing

It is an important part of a tester’s role to be familiar with the common software development lifecycle models so that appropriate test activities can take place.

In any software development lifecycle model, there are several characteristics of good testing:

  • For every development activity, there is a corresponding test activity
  • Each test level has test objectives specific to that level
  • Test analysis and design for a given test level begin during the corresponding development activity
  • Testers participate in discussions to define and refine requirements and design, and are involved in reviewing work products (e.g., requirements, design, user stories, etc.) as soon as drafts are available

No matter which software development lifecycle model is chosen, test activities should start in the early stages of the lifecycle, adhering to the testing principle of early testing.

This article categories common software development lifecycle models as follows:

  • Sequential development models
  • Iterative and incremental development models

A sequential development model describes the software development process as a linear, sequential flow of activities. This means that any phase in the development process should begin when the previous phase is complete. In theory, there is no overlap of phases, but in practice, it is beneficial to have early feedback from the following phase.

In the Waterfall model, the development activities (e.g., requirements analysis, design, coding, testing) are completed one after another. In this model, test activities only occur after all other development activities have been completed.

Unlike the Waterfall model, the V-model integrates the test process throughout the development process, implementing the principle of early testing. Further, the V-model includes test levels associated with each corresponding development phase, which further supports early testing. In this model, the execution of tests associated with each test level proceeds sequentially, but in some cases overlapping occurs.

Sequential development models deliver software that contains the complete set of features, but typically require months or years for delivery to stakeholders and users.

Incremental development involves establishing requirements, designing, building, and testing a system in pieces, which means that the software’s features grow incrementally. The size of these feature increments varies, with some methods having larger pieces and some smaller pieces. The feature increments can be as small as a single change to a user interface screen or new query option.

Iterative development occurs when groups of features are specified, designed, built, and tested together in a series of cycles, often of a fixed duration. Iterations may involve changes to features developed in earlier iterations, along with changes in project scope. Each iteration delivers working software which is a growing subset of the overall set of features until the final software is delivered or development is stopped.

Examples include: 

  • Rational Unified Process: Each iteration tends to be relatively long (e.g., two to three months), and the feature increments are correspondingly large, such as two or three groups of related features
  • Scrum: Each iteration tends to be relatively short (e.g., hours, days, or a few weeks), and the feature increments are correspondingly small, such as a few enhancements and/or two or three new features
  • Kanban: Implemented with or without fixed-length iterations, which can deliver either a single enhancement or feature upon completion, or can group features together to release at once
  • Spiral: Involves creating experimental increments, some of which may be heavily re-worked or even abandoned in subsequent development work

Components or systems developed using these methods often involve overlapping and iterating test levels throughout development. Ideally, each feature is tested at several test levels as it moves towards delivery. In some cases, teams use continuous delivery or continuous deployment, both of which involve significant automation of multiple test levels as part of their delivery pipelines. Many development efforts using these methods also include the concept of self-organising teams, which can change the way testing work is organised as well as the relationship between testers and developers.

These methods form a growing system, which may be released to end-users on a feature-by-feature basis, on an iteration-by-iteration basis, or in a more traditional major-release fashion. Regardless of whether the software increments are released to end-users, regression testing is increasingly important as the system grows.

In contrast to sequential models, iterative and incremental models may deliver usable software in weeks or even days, but may only deliver the complete set of requirements product over a period of months or even years.

Software Development Lifecycle Models in Context

Software development lifecycle models must be selected and adapted to the context of project and product characteristics. An appropriate software development lifecycle model should be selected and adapted based on the project goal, the type of product being developed, business priorities (e.g., time-to-market), and identified product and project risks. For example, the development and testing of a minor internal administrative system should differ from the development and testing of a safety-critical system such as an automobile’s brake control system. As another example, in some cases organisational and cultural issues may inhibit communication between team members, which can impede iterative development.

Depending on the context of the project, it may be necessary to combine or reorganise test levels and/or test activities. For example, for the integration of a commercial off-the-shelf (COTS) software product into a larger system, the purchaser may perform interoperability testing at the system integration test level (e.g., integration to the infrastructure and other systems) and at the acceptance test level (functional and non-functional, along with user acceptance testing and operational acceptance testing).

In addition, software development lifecycle models themselves may be combined. For example, a V-model may be used for the development and testing of the backend systems and their integrations, while an Agile development model may be used to develop and test the front-end user interface (UI) and functionality. Prototyping may be used early in a project, with an incremental development model adopted once the experimental phase is complete. 

Internet of Things (IoT) systems, which consist of many different objects, such as devices, products, and services, typically apply separate software development lifecycle models for each object. This presents a particular challenge for the development of Internet of Things system versions. Additionally the software development lifecycle of such objects places stronger emphasis on the later phases of the software development lifecycle after they have been introduced to operational use (e.g., operate, update, and decommission phases). 

Reasons why software development models must be adapted to the context of project and product characteristics can be:

  • Difference in product risks of systems (complex or simple project)
  • Many business units can be part of a project or program (combination of sequential and agile development)
  • Short time to deliver a product to the market (merge of test levels and/or integration of test types in test levels)

Test Levels

Test levels are groups of test activities that are organised and managed together. Each test level is an instance of the test process, consisting of the activities described in the basics of testing article, performed in relation to software at a given level of development, from individual units or components to complete systems or, where applicable, systems of systems. Test levels are related to other activities within the software development lifecycle. The test levels used in this article are:

  • Component testing
  • Integration testing
  • System testing
  • Acceptance testing

Test levels are characterised by the following attributes:

  • Specific objectives
  • Test basis, referenced to derive test cases
  • Test object (i.e., what is being tested)
  • Typical defects and failures
  • Specific approaches and responsibilities

For every test level, a suitable test environment is required. In acceptance testing, for example, a production-like test environment is ideal, while in component testing the developers typically use their own development environment.

Component Testing

Objectives of component testing

Component testing (also known as unit or module testing) focuses on components that are separately testable. Objectives of component testing include:

  • Reducing risks
  • Verifying whether the functional and non-functional behaviours of the component are as designed and specified
  • Building confidence in the component’s quality
  • Finding defects in the component
  • Preventing defects from escaping to higher test levels

In some cases, especially in incremental and iterative development models (e.g., Agile) where code changes are ongoing, automated component regression tests play a key role in building confidence that changes have not broken existing components.

Component testing is often done in isolation from the rest of the system, depending on the software development lifecycle model and the system, which may require mock objects, service virtualisation, harnesses, stubs, and drivers. Component testing may cover functionality (e.g., correctness of calculations), non-functional characteristics (e.g., searching for memory leaks), and structural properties (e.g., decision testing).

Test basis

Examples of work products that can be used as a test basis for component testing include:

  • Detailed design
  • Code
  • Data model 
  • Component specifications

Test objects

Typical test objects for component testing include:

  • Components, units or modules
  • Code and data structures
  • Classes
  • Database modules

Typical defects and failures

Examples of typical defects and failures for component testing include:

  • Incorrect functionality (e.g., not as described in design specifications)
  • Data flow problems
  • Incorrect in the code and/or logic

Defects are typically fixed as soon as they are found, often with no formal defect management. However, when developers do report defects, this provides important information for root cause analysis and process improvement.

Specific approaches and responsibilities

Component testing is usually performed by the developer who wrote the code, but it at least requires access to the code being tested. Developers may alternate component development with finding and fixing defects. Developers will often write and execute tests after having written the code for a component. However, in Agile development especially, writing automated component test cases may precede writing application code. 

For example, consider test driven development (TDD). Test driven development is highly iterative and is based on cycles of developing automated test cases, then building and integrating small pieces of code, then executing the component tests, correcting any issues, and re-factoring the code. This process continues until the component has been completely built and all component tests are passing. Test driven development is an example of a test-first approach. While test driven development originated in eXtreme Programming (XP), it has spread to other forms of Agile and also to sequential lifecycles.

Integration Testing

Objectives of integration testing

Integration testing focuses on interactions between components or systems. Objectives of integration testing include:

  • Reducing risks
  • Verifying whether the functional and non-functional behaviours of the interfaces are as designed and specified
  • Building confidence in the quality of the interfaces
  • Finding defects (which may be in the interfaces themselves or within the components or systems)
  • Preventing defects from escaping to higher test levels

As with component testing, in some cases automated integration regression tests provide confidence that changes have not broken existing interfaces, components, or systems.

There are two different levels of integration testing described in this article, which may be carried out on test objects of varying size as follows:

  • Component integration testing focuses on the interactions and interfaces between integrated components. Component integration testing is performed after component testing, and is generally automated. In iterative and incremental development, component integration tests are usually part of the continuous integration process.
  • System integration testing focuses on the interactions and interfaces between systems, packages, and micro-services. System integration testing can also cover interactions with, and interfaces provided by external organisations (e.g., web services). In this case, the developing organisation does not control the external interfaces, which can create various challenges for testing (e.g., ensuring that test-blocking defects in the external organisation’s code are resolved, arranging for test environments, etc.). System integration testing may be done after system testing or in parallel with ongoing system test activities (in both sequential development and iterative and incremental development).

Test basis

Examples of work products that can be used as a test basis for integration testing include:

  • Software and system design
  • Sequence diagrams
  • Interface and communication protocol specifications
  • Use cases
  • Architecture at component or system level
  • Workflows
  • External interface definitions

Test objects

Typical test objects for integration testing include:

  • Subsystems
  • Databases
  • Infrastructure
  • Interfaces
  • APIs
  • Microservices

Typical defects and failures

Examples of typical defects and failures for component integration testing include:

  • Incorrect data, missing data, or incorrect data encoding
  • Incorrect sequencing or timing of interface calls
  • Interface mismatch
  • Failures in communication between components
  • Unhandled or improperly handled communication failures between components
  • Incorrect assumptions about the meaning, units, or boundaries of the data being passed between components

Examples of typical defects and failures for system integration testing include: 

  • Inconsistent message structures between systems
  • Incorrect data, missing data, or incorrect data encoding
  • Interface mismatch
  • Failures in communication between systems
  • Unhandled or improperly handled communication failures between systems
  • Incorrect assumptions about the meaning, units, or boundaries of the data being passed between systems
  • Failure to comply with mandatory security regulations

Specific approaches and responsibilities

Component integration tests and system integration tests should concentrate on the integration itself. For example, if integrating module A with module B, tests should focus on the communication between the modules, not the functionality of the individual modules, as that should have been covered during component testing. If integrating system X with system Y, tests should focus on the communication between the systems, not the functionality of the individual systems, as that should have been covered during system testing. Functional, non-functional, and structural test types are applicable.

Component integration testing is often the responsibility of developers. System integration testing is generally the responsibility of testers. Ideally, testers performing system integration testing should understand the system architecture, and should have influenced integration planning.

If integration tests and the integration strategy are planned before components or systems are built, those components or systems can be built in the order required for most efficient testing. Systematic integration strategies may be based on the system architecture (e.g., top-down and bottom-up), functional tasks, transaction processing sequences, or some other aspect of the system or components. In order to simplify defect isolation and detect defects early, integration should normally be incremental (i.e., a small number of additional components or systems at a time) rather than “big bang” (i.e., integrating all components or systems in one single step). A risk analysis of the most complex interfaces can help to focus the integration testing.

The greater the scope of integration, the more difficult it becomes to isolate defects to a specific component or system, which may lead to increased risk and additional time for troubleshooting. This is one reason that continuous integration, where software is integrated on a component-by-component basis (i.e., functional integration), has become common practice. Such continuous integration often includes automated regression testing, ideally at multiple test levels.

System Testing

Objectives of system testing

System testing focuses on the behaviour and capabilities of a whole system or product, often considering the end-to-end tasks the system can perform and the non-functional behaviours it exhibits while performing those tasks. Objectives of system testing include:

  • Reducing risks
  • Verifying whether the functional and non-functional behaviours of the system are as designed and specified
  • Validating that the system is complete and will work as expected
  • Building confidence in the quality of the system as a whole
  • Finding defects
  • Preventing defects from escaping to higher test levels or production

For certain systems, verifying data quality may also be an objective. As with component testing and integration testing, in some cases automated system regression tests provide confidence that changes have not broken existing features or end-to-end capabilities. System testing often produces information that is used by stakeholders to make release decisions. System testing may also satisfy legal or regulatory requirements or standards.

The test environment should ideally correspond to the final target or production environment.

Test basis

Examples of work products that can be used as a test basis for system testing include:

  • System and software requirement specifications (functional and non-functional)
  • Risk analysis reports
  • Use cases
  • Epics and user stories
  • Models of system behaviour
  • State diagrams
  • System and user manuals

Test objects

Typical test objects for system testing include:

  • Applications
  • Hardware/software systems
  • Operating systems
  • System under test (SUT)
  • System configuration and configuration data

Typical defects and failures

Examples of typical defects and failures for system testing include:

  • Incorrect calculations
  • Incorrect or unexpected system functional or non-functional behaviour
  • Incorrect control and/or data flows within the system
  • Failure to properly and completely carry out end-to-end functional tasks
  • Failure of the system to work properly in the system environment(s)
  • Failure of the system to work as described in system and user manuals

Specific approaches and responsibilities

System testing should focus on the overall, end-to-end behaviour of the system as a whole, both functional and non-functional. System testing should use the most appropriate techniques (see test techniques) for the aspect(s) of the system to be tested. For example, a decision table may be created to verify whether functional behaviour is as described in business rules.

System testing is typically carried out by independent testers who rely heavily on specifications. Defects in specifications (e.g., missing user stories, incorrectly stated business requirements, etc.) can lead to a lack of understanding of, or disagreements about, expected system behaviour. Such situations can cause false positives and false negatives, which waste time and reduce defect detection effectiveness, respectively. Early involvement of testers in user story refinement or static testing activities, such as reviews, helps to reduce the incidence of such situations.

Acceptance Testing

Objectives of acceptance testing

Acceptance testing, like system testing, typically focuses on the behaviour and capabilities of a whole system or product. Objectives of acceptance testing include:

  • Establishing confidence in the quality of the system as a whole
  • Validating that the system is complete and will work as expected
  • Verifying that functional and non-functional behaviours of the system are as specified

Acceptance testing may produce information to assess the system’s readiness for deployment and use by the customer (end-user). Defects may be found during acceptance testing, but finding defects is often not an objective, and finding a significant number of defects during acceptance testing may in some cases be considered a major project risk. Acceptance testing may also satisfy legal or regulatory requirements or standards.

Common forms of acceptance testing include the following:

  • User acceptance testing
  • Operational acceptance testing
  • Contractual and regulatory acceptance testing
  • Alpha and beta testing.

Each is described in the following four subsections.

User acceptance testing (UAT)

User acceptance testing of the system is typically focused on validating the fitness for use of the system by intended users in a real or simulated operational environment. The main objective is building confidence that the users can use the system to meet their needs, fulfil requirements, and perform business processes with minimum difficulty, cost, and risk.

Operational acceptance testing (OAT)

The acceptance testing of the system by operations or systems administration staff is usually performed in a (simulated) production environment. The tests focus on operational aspects, and may include:

  • Testing of backup and restore
  • Installing, uninstalling and upgrading
  • Disaster recovery
  • User management
  • Maintenance tasks
  • Data load and migration tasks
  • Checks for security vulnerabilities
  • Performance testing

The main objective of operational acceptance testing is building confidence that the operators or system administrators can keep the system working properly for the users in the operational environment, even under exceptional or difficult conditions.

Contractual and regulatory acceptance testing

Contractual acceptance testing is performed against a contract’s acceptance criteria for producing custom-developed software. Acceptance criteria should be defined when the parties agree to the contract. Contractual acceptance testing is often performed by users or by independent testers.

Regulatory acceptance testing is performed against any regulations that must be adhered to, such as government, legal, or safety regulations. Regulatory acceptance testing is often performed by users or by independent testers, sometimes with the results being witnessed or audited by regulatory agencies.

The main objective of contractual and regulatory acceptance testing is building confidence that contractual or regulatory compliance has been achieved.

Alpha and beta testing

Alpha and beta testing are typically used by developers of commercial off-the-shelf (COTS) software who want to get feedback from potential or existing users, customers, and/or operators before the software product is put on the market. Alpha testing is performed at the developing organisation’s site, not by the development team, but by potential or existing customers, and/or operators or an independent test team. Beta testing is performed by potential or existing customers, and/or operators at their own locations. Beta testing may come after alpha testing, or may occur without any preceding alpha testing having occurred. 

One objective of alpha and beta testing is building confidence among potential or existing customers, and/or operators that they can use the system under normal, everyday conditions, and in the operational environment(s) to achieve their objectives with minimum difficulty, cost, and risk. Another objective may be the detection of defects related to the conditions and environment(s) in which the system will be used, especially when those conditions and environment(s) are difficult to replicate by the development team.

Test basis

Examples of work products that can be used as a test basis for any form of acceptance testing include:

  • Business processes
  • User or business requirements
  • Regulations, legal contract and/or standards
  • Use cases and/or user stories
  • System requirements
  • System or user documentation
  • Installation procedures
  • Risk analysis reports

In addition, as a test basis for deriving test cases for operational acceptance testing, one or more of the following work products can be used:

  • Backup and restore procedures
  • Disaster recovery procedures
  • Non-functional requirements
  • Operations documentation
  • Deployment and installation instructions
  • Performance targets
  • Database packages
  • Security standards or regulations

Typical test objects

Typical test objects for any form of acceptance testing include:

  • System under test
  • System configuration and configuration data
  • Business processes for a fully integrated system
  • Recovery systems and hot sites (for business continuity and disaster recovery testing)
  • Operational and maintenance processes
  • Forms
  • Reports
  • Existing and converted production data

Typical defects and failures

Examples of typical defects for any form of acceptance testing include:

  • System workflows do not meet business or user requirements
  • Business rules are not implemented correctly
  • System does not satisfy contractual or regulatory requirements
  • Non-functional failures such as security vulnerabilities, inadequate performance efficiency under high loads, or improper operation on a supported platform

Specific approaches and responsibilities

Acceptance testing is often the responsibility of the customers, business users, product owners, or operators of a system, and other stakeholders may be involved as well.

Acceptance testing is often thought of as the last test level in a sequential development lifecycle, but it may also occur at other times, for example:

  • Acceptance testing of a COTS software product may occur when it is installed or integrated
  • Acceptance testing of a new functional enhancement may occur before system testing

In iterative development, project teams can employ various forms of acceptance testing during and at the end of each iteration, such as those focused on verifying a new feature against its acceptance criteria and those focused on validating that a new feature satisfies the users’ needs. In addition, alpha tests and beta tests may occur, either at the end of each iteration, after the completion of each iteration, or after a series of iterations. User acceptance tests, operational acceptance tests, regulatory acceptance tests, and contractual acceptance tests also may occur, either at the close of each iteration, after the completion of each iteration, or after a series of iterations.

Test Types

A test type is a group of test activities aimed at testing specific characteristics of a software system, or a part of a system, based on specific test objectives. Such objectives may include:

  • Evaluating functional quality characteristics, such as completeness, correctness, and appropriateness
  • Evaluating non-functional quality characteristics, such as reliability, performance efficiency, security, compatibility, and usability
  • Evaluating whether the structure or architecture of the component or system is correct, complete, and as specified
  • Evaluating the effects of changes, such as confirming that defects have been fixed (confirmation testing) and looking for unintended changes in behaviour resulting from software or environment changes (regression testing)

Functional Testing

Functional testing of a system involves tests that evaluate functions that the system should perform. Functional requirements may be described in work products such as business requirements specifications, epics, user stories, use cases, or functional specifications, or they may be undocumented. The functions are “what” the system should do. 

Functional tests should be performed at all test levels (e.g., tests for components may be based on a component specification), though the focus is different at each level. 

Functional testing considers the behaviour of the software, so black-box techniques may be used to derive test conditions and test cases for the functionality of the component or system. 

The thoroughness of functional testing can be measured through functional coverage. Functional coverage is the extent to which some functionality has been exercised by tests, and is expressed as a percentage of the type(s) of element being covered. For example, using traceability between tests and functional requirements, the percentage of these requirements which are addressed by testing can be calculated, potentially identifying coverage gaps.

Functional test design and execution may involve special skills or knowledge, such as knowledge of the particular business problem the software solves (e.g., geological modelling software for the oil and gas industries). 

Non-functional Testing

Non-functional testing of a system evaluates characteristics of systems and software such as usability, performance efficiency or security. Non-functional testing is the testing of “how well” the system behaves. 

Contrary to common misperceptions, non-functional testing can and often should be performed at all test levels, and done as early as possible. The late discovery of non-functional defects can be extremely dangerous to the success of a project. 

Black-box techniques may be used to derive test conditions and test cases for non-functional testing. For example, boundary value analysis can be used to define the stress conditions for performance tests. 

The thoroughness of non-functional testing can be measured through non-functional coverage. Non-functional coverage is the extent to which some type of non-functional element has been exercised by tests, and is expressed as a percentage of the type(s) of element being covered. For example, using traceability between tests and supported devices for a mobile application, the percentage of devices which are addressed by compatibility testing can be calculated, potentially identifying coverage gaps. 

Non-functional test design and execution may involve special skills or knowledge, such as knowledge of the inherent weaknesses of a design or technology (e.g., security vulnerabilities associated with particular programming languages) or the particular user base (e.g., the personas of users of healthcare facility management systems).

White-box Testing

White-box testing derives tests based on the system’s internal structure or implementation. Internal structure may include code, architecture, work flows, and/or data flows within the system. 

The thoroughness of white-box testing can be measured through structural coverage. Structural coverage is the extent to which some type of structural element has been exercised by tests, and is expressed as a percentage of the type of element being covered. 

At the component testing level, code coverage is based on the percentage of component code that has been tested, and may be measured in terms of different aspects of code (coverage items) such as the percentage of executable statements tested in the component, or the percentage of decision outcomes tested. These types of coverage are collectively called code coverage. At the component integration testing level, white-box testing may be based on the architecture of the system, such as interfaces between components, and structural coverage may be measured in terms of the percentage of interfaces exercised by tests. 

White-box test design and execution may involve special skills or knowledge, such as the way the code is built, how data is stored (e.g., to evaluate possible database queries), and how to use coverage tools and to correctly interpret their results.

Change-related Testing

When changes are made to a system, either to correct a defect or because of new or changing functionality, testing should be done to confirm that the changes have corrected the defect or implemented the functionality correctly, and have not caused any unforeseen adverse consequences.

  • Confirmation testing: After a defect is fixed, the software may be tested with all test cases that failed due to the defect, which should be re-executed on the new software version. The software may also be tested with new tests to cover changes needed to fix the defect. At the very least, the steps to reproduce the failure(s) caused by the defect must be re-executed on the new software version. The purpose of a confirmation test is to confirm whether the original defect has been successfully fixed.
  • Regression testing: It is possible that a change made in one part of the code, whether a fix or another type of change, may accidentally affect the behaviour of other parts of the code, whether within the same component, in other components of the same system, or even in other systems. Changes may include changes to the environment, such as a new version of an operating system or database management system. Such unintended side-effects are called regressions. Regression testing involves running tests to detect such unintended side-effects.

Confirmation testing and regression testing are performed at all test levels.

Especially in iterative and incremental development lifecycles (e.g., Agile), new features, changes to existing features, and code refactoring result in frequent changes to the code, which also requires change-related testing. Due to the evolving nature of the system, confirmation and regression testing are very important. This is particularly relevant for Internet of Things systems where individual objects (e.g., devices) are frequently updated or replaced.

Regression test suites are run many times and generally evolve slowly, so regression testing is a strong candidate for automation. Automation of these tests should start early in the project.

Test Types and Test Levels

It is possible to perform any of the test types mentioned above at any test level. To illustrate, examples of functional, non-functional, white-box, and change-related tests will be given across all test levels, for a banking application, starting with functional tests: 

  • For component testing, tests are designed based on how a component should calculate compound interest.
  • For component integration testing, tests are designed based on how account information captured at the user interface is passed to the business logic.
  • For system testing, tests are designed based on how account holders can apply for a line of credit on their checking accounts.
  • For system integration testing, tests are designed based on how the system uses an external micro-service to check an account holder’s credit score.
  • For acceptance testing, tests are designed based on how the banker handles approving or declining a credit application.

The following are examples of non-functional tests:

  • For component testing, performance tests are designed to evaluate the number of CPU cycles required to perform a complex total interest calculation. 
  • For component integration testing, security tests are designed for buffer overflow vulnerabilities due to data passed from the user interface to the business logic. 
  • For system testing, portability tests are designed to check whether the presentation layer works on all supported browsers and mobile devices. 
  • For system integration testing, reliability tests are designed to evaluate system robustness if the credit score micro-service fails to respond. 
  • For acceptance testing, usability tests are designed to evaluate the accessibility of the banker’s credit processing interface for people with disabilities.

The following are examples of white-box tests:

  • For component testing, tests are designed to achieve complete statement and decision coverage for all components that perform financial calculations. 
  • For component integration testing, tests are designed to exercise how each screen in the browser interface passes data to the next screen and to the business logic.
  • For system testing, tests are designed to cover sequences of web pages that can occur during a credit line application.
  • For system integration testing, tests are designed to exercise all possible inquiry types sent to the credit score micro-service.
  • For acceptance testing, tests are designed to cover all supported financial data file structures and value ranges for bank-to-bank transfers.

Finally, the following are examples for change-related tests:

  • For component testing, automated regression tests are built for each component and included within the continuous integration framework.
  • For component integration testing, tests are designed to confirm fixes to interface-related defects as the fixes are checked into the code repository.
  • For system testing, all tests for a given workflow are re-executed if any screen on that workflow changes.
  • For system integration testing, tests of the application interacting with the credit scoring micro-service are re-executed daily as part of continuous deployment of that micro-service.
  • For acceptance testing, all previously failed tests are re-executed after a defect found in acceptance testing is fixed.

While this section provides examples of every test type across every level, it is not necessary, for all software, to have every test type represented across every level. However, it is important to run applicable test types at each level, especially the earliest level where the test type occurs.

Maintenance Testing

Once deployed to production environments, software and systems need to be maintained. Changes of various sorts are almost inevitable in delivered software and systems, either to fix defects discovered in operational use, to add new functionality, or to delete or alter already-delivered functionality. Maintenance is also needed to preserve or improve non-functional quality characteristics of the component or system over its lifetime, especially performance efficiency, compatibility, reliability, security, and portability. 

When any changes are made as part of maintenance, maintenance testing should be performed, both to evaluate the success with which the changes were made and to check for possible side-effects (e.g., regressions) in parts of the system that remain unchanged (which is usually most of the system). Maintenance can involve planned releases and unplanned releases (hot fixes). 

A maintenance release may require maintenance testing at multiple test levels, using various test types, based on its scope. The scope of maintenance testing depends on: 

  • The degree of risk of the change, for example, the degree to which the changed area of software communicates with other components or systems
  • The size of the existing system
  • The size of the change

Triggers for Maintenance

There are several reasons why software maintenance, and thus maintenance testing, takes place, both for planned and unplanned changes. 

We can classify the triggers for maintenance as follows: 

  • Modification, such as planned enhancements (e.g., release-based), corrective and emergency changes, changes of the operational environment (such as planned operating system or database upgrades), upgrades of COTS software, and patches for defects and vulnerabilities
  • Migration, such as from one platform to another, which can require operational tests of the new environment as well as of the changed software, or tests of data conversion when data from another application will be migrated into the system being maintained
    • Retirement, such as when an application reaches the end of its life. When an application or system is retired, this can require testing of data migration or archiving if long data-retention periods are required. 
    • Testing restored/retrieve procedures after archiving for long retention periods may also be needed. 
    • Regression testing may be needed to ensure that any functionality that remains in service still works. 

For Internet of Things systems, maintenance testing may be triggered by the introduction of completely new or modified things, such as hardware devices and software services, into the overall system. The maintenance testing for such systems places particular emphasis on integration testing at different levels (e.g., network level, application level) and on security aspects, in particular those relating to personal data. 

Impact Analysis for Maintenance

Impact analysis evaluates the changes that were made for a maintenance release to identify the intended consequences as well as expected and possible side effects of a change, and to identify the areas in the system that will be affected by the change. Impact analysis can also help to identify the impact of a change on existing tests. The side effects and affected areas in the system need to be tested for regressions, possibly after updating any existing tests affected by the change. 

Impact analysis may be done before a change is made, to help decide if the change should be made, based on the potential consequences in other areas of the system. 

Impact analysis can be difficult if: 

  • Specifications (e.g., business requirements, user stories, architecture) are out of date or missing
  • Test cases are not documented or are out of date
  • Bi-directional traceability between tests and the test basis has not been maintained
  • Tool support is weak or non-existent
  • The people involved do not have domain and/or system knowledge
  • Insufficient attention has been paid to the software’s maintainability during development

Testing throughout the software development lifecycle

A software development lifecycle model describes the types of activity performed at each stage in a software development project, and how the activities relate to one another logically and chronologically. There are a number of different software development lifecycle models, each of which requires different approaches to testing.

Software development and software testing

It is an important part of a tester’s role to be familiar with the common software development lifecycle models so that appropriate test activities can take place.

In any software development lifecycle model, there are several characteristics of good testing:

  • For every development activity, there is a corresponding test activity
  • Each test level has test objectives specific to that level
  • Test analysis and design for a given test level begin during the corresponding development activity
  • Testers participate in discussions to define and refine requirements and design, and are involved in reviewing work products (e.g., requirements, design, user stories, etc.) as soon as drafts are available

No matter which software development lifecycle model is chosen, test activities should start in the early stages of the lifecycle, adhering to the testing principle of early testing.

This categorizes common software development lifecycle models as follows:

  • Sequential development models
  • Iterative and incremental development models

A sequential development model describes the software development process as a linear, sequential flow of activities. This means that any phase in the development process should begin when the previous phase is complete. In theory, there is no overlap of phases, but in practice, it is beneficial to have early feedback from the following phase.

In the Waterfall model, the development activities (e.g., requirements analysis, design, coding, testing) are completed one after another. In this model, test activities only occur after all other development activities have been completed.

Unlike the Waterfall model, the V-model integrates the test process throughout the development process, implementing the principle of early testing. Further, the V-model includes test levels associated with each corresponding development phase, which further supports early testing. In this model, the execution of tests associated with each test level proceeds sequentially, but in some cases overlapping occurs.

Sequential development models deliver software that contains the complete set of features, but typically require months or years for delivery to stakeholders and users.

Incremental development involves establishing requirements, designing, building, and testing a system in pieces, which means that the software’s features grow incrementally. The size of these feature increments varies, with some methods having larger pieces and some smaller pieces. The feature increments can be as small as a single change to a user interface screen or new query option.

Iterative development occurs when groups of features are specified, designed, built, and tested together in a series of cycles, often of a fixed duration. Iterations may involve changes to features developed in earlier iterations, along with changes in project scope. Each iteration delivers working software which is a growing subset of the overall set of features until the final software is delivered or development is stopped.

Examples include:

  • Rational Unified Process: Each iteration tends to be relatively long (e.g., two to three months), and the feature increments are correspondingly large, such as two or three groups of related features
  • Scrum: Each iteration tends to be relatively short (e.g., hours, days, or a few weeks), and the feature increments are correspondingly small, such as a few enhancements and/or two or three new features
  • Kanban: Implemented with or without fixed-length iterations, which can deliver either a single enhancement or feature upon completion, or can group features together to release at once
  • Spiral: Involves creating experimental increments, some of which may be heavily re-worked or even abandoned in subsequent development work

Components or systems developed using these methods often involve overlapping and iterating test levels throughout development. Ideally, each feature is tested at several test levels as it moves towards delivery. In some cases, teams use continuous delivery or continuous deployment, both of which involve significant automation of multiple test levels as part of their delivery pipelines. Many development efforts using these methods also include the concept of self-organizing teams, which can change the way testing work is organized as well as the relationship between testers and developers.

These methods form a growing system, which may be released to end-users on a feature-by-feature basis, on an iteration-by-iteration basis, or in a more traditional major-release fashion. Regardless of whether the software increments are released to end-users, regression testing is increasingly important as the system grows.

In contrast to sequential models, iterative and incremental models may deliver usable software in weeks or even days, but may only deliver the complete set of requirements product over a period of months or even years.

Software development lifecycle models in context

Software development lifecycle models must be selected and adapted to the context of project and product characteristics. An appropriate software development lifecycle model should be selected and adapted based on the project goal, the type of product being developed, business priorities (e.g., time-to- market), and identified product and project risks. For example, the development and testing of a minor internal administrative system should differ from the development and testing of a safety-critical system such as an automobile’s brake control system. As another example, in some cases organizational and cultural issues may inhibit communication between team members, which can impede iterative development.

Depending on the context of the project, it may be necessary to combine or reorganize test levels and/or test activities. For example, for the integration of a commercial off-the-shelf (COTS) software product into a larger system, the purchaser may perform interoperability testing at the system integration test level (e.g., integration to the infrastructure and other systems) and at the acceptance test level (functional and non-functional, along with user acceptance testing and operational acceptance testing).

In addition, software development lifecycle models themselves may be combined. For example, a V- model may be used for the development and testing of the backend systems and their integrations, while an Agile development model may be used to develop and test the front-end user interface (UI) and functionality. Prototyping may be used early in a project, with an incremental development model adopted once the experimental phase is complete.

Internet of Things (IoT) systems, which consist of many different objects, such as devices, products, and services, typically apply separate software development lifecycle models for each object. This presents a particular challenge for the development of Internet of Things system versions. Additionally the software development lifecycle of such objects places stronger emphasis on the later phases of the software development lifecycle after they have been introduced to operational use (e.g., operate, update, and decommission phases).

Reasons why software development models must be adapted to the context of project and product characteristics can be:

  • Difference in product risks of systems (complex or simple project)
  • Many business units can be part of a project or program (combination of sequential and agile development)
  • Short time to deliver a product to the market (merge of test levels and/or integration of test types in test levels)