Software testing is easiest to understand as three intersecting dimensions: level (what scope is tested), objective (what behavior or quality is evaluated), and approach (how the test is performed). A test can be described on all three at once—for example, automated functional testing at system level. This avoids treating terms that answer different questions as competing items in one list.
How the main testing categories fit together
This guide follows the introductory taxonomy in the ISTQB Certified Tester Foundation Level Syllabus v4.0.1, dated September 15, 2024. Standards and industry vocabularies can use terms differently, so name the framework when precision matters. The ISO/IEC/IEEE 29119 series offers a standards framework for software testing; its overview describes the series as intended for use by any organization performing any form of software testing (ISO/IEC/IEEE 29119 series).
| Dimension | Question it answers | Examples |
|---|---|---|
| Level | What is the scope or test object? | Component, integration, system, acceptance |
| Objective or type | What behavior or quality is evaluated? | Functional, non-functional |
| Approach | How is testing performed? | Manual or automated; scripted or unscripted; static or dynamic |
These dimensions are not mutually exclusive. A team might conduct manual, non-functional testing at system level, or automated functional testing at component-integration level.
What are the levels of software testing?
Test levels distinguish scope and test object. ISTQB identifies component (also called unit), component integration, system, system integration, and acceptance testing. The labels are useful, but the test object and objective are what make a test meaningful.
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Random freezes, missing sound and display glitches usually trace back to one bad driver. Find and replace yours safely.Free scan · under a minute| Level | Typical test object | Main question | Example |
|---|---|---|---|
| Component (unit) | An individual component or unit | Does this isolated part behave as expected? | Check that a tax-calculation function returns the expected result for defined inputs. |
| Component integration | Interactions among components | Do connected components exchange data and work together correctly? | Check that a checkout service passes an order to the payment component in the expected format. |
| System | A complete integrated system | Does the system meet its specified requirements? | Test an end-to-end order flow within the application. |
| System integration | Interfaces between the system and other systems or services | Does the system work correctly with external systems? | Check that an application handles a response from a payment provider as expected. |
| Acceptance | A system or solution considered against business needs and readiness criteria | Is it acceptable for its intended use or release? | Have intended users validate that a workflow supports their business process. |
Component and integration levels
Component testing focuses on an individual unit; component-integration testing focuses on interactions among components. System-integration testing is different: it checks connections between the system under test and other systems or services. A failure at an interface may arise even when the connected components work individually, which is why the scope of the test matters.
System testing
System testing evaluates the integrated system against requirements. Its objective can be functional or non-functional; “system” identifies the level, not the quality being checked.
Acceptance testing
Acceptance testing is validation against business needs and readiness, not simply another name for system testing. ISTQB identifies user, operational, contractual, and regulatory acceptance testing, as well as alpha and beta testing, among its forms. The appropriate form depends on who is accepting the system and which needs or obligations are being evaluated. See the ISTQB syllabus for the framework’s definitions.
Functional and non-functional testing
These types describe the objective, not the level. The same objective can be tested at more than one level.
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| Type | What it evaluates | Illustrative question |
|---|---|---|
| Functional | What a component or system should do | Does submitting a valid order create an order record? |
| Non-functional | How well a component or system behaves against quality characteristics | Does the system remain responsive under its intended operating conditions? |
ISTQB points to ISO/IEC 25010 for classifying non-functional quality characteristics. Choose the characteristic relevant to the product and its context rather than treating “non-functional” as one specific test. A test may assess a quality such as performance, security, or usability, but the criteria and conditions need to be defined for that product.
Testing approaches: execution, visibility, and test basis
Manual and automated
Manual testing is performed by a person executing or evaluating test activities; automated testing uses tools or scripts to execute tests or assess results. ISO/IEC/IEEE 29119-2 supports both approaches. The choice depends on the test objective and context; automation does not itself define what is being tested.
Scripted and unscripted
Scripted tests follow prepared instructions or procedures. Unscripted testing leaves more room to adapt the investigation while testing. These describe how the work is guided, and either may be performed manually or with tools as appropriate. They are not substitutes for naming the test level or objective.
Static and dynamic
Static testing evaluates work products without executing the software—for example, reviewing requirements or code. Dynamic testing exercises the software by running it. They describe whether execution is involved; they do not tell you whether the test is functional, non-functional, or at a particular level.
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Black-box and white-box
Black-box techniques derive tests from externally observable behavior or a test basis such as requirements, without relying on internal implementation details. White-box techniques use knowledge of internal structure to design or assess tests. These are ways of selecting or analyzing tests, not test levels. A practical test strategy may use both.
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Retesting and regression testing
Retesting and regression testing are change-related strategy terms, not additional test levels. Apply change-related tests at the scope where the change and its risks lie. ISTQB and the ISO series overview include these concepts in testing strategy, but the overview alone does not establish a complete distinction among regression, confirmation testing, and retesting. Use the terminology defined by the testing framework or organization you follow, and state the intended purpose in the test plan.
How to choose the right testing mix
Not every product needs every level in the same way. The ISO/IEC/IEEE 29119 overview notes that testing at all levels is not always necessary, while a usual sequence generally remains. Tailor the plan to the test object, objectives, risks, and environment rather than applying a rigid checklist (ISO/IEC/IEEE 29119 series).
- Name the test object and scope. Decide whether the question concerns one component, interactions among components, the integrated system, external interfaces, or acceptance against business needs.
- State the objective. Specify the function or quality characteristic being evaluated and the observable result that would meet the criterion.
- Assess risk and consequences. Give attention to failure modes with meaningful impact, including critical user or business workflows and important interfaces.
- Check dependencies and environment. Determine whether the test needs realistic external services, data, permissions, devices, or operating conditions. A simulated dependency may speed feedback, but it cannot by itself establish behavior against a live service.
- Choose an execution approach. Consider whether a manual or automated, scripted or unscripted, static or dynamic approach suits the objective. Speed, maintenance effort, and feedback timing depend on the implementation; they are practical trade-offs rather than universal properties of a test category.
- Record boundaries and evidence. Document what was tested, under which conditions, against which criteria, and what remains outside the test. This helps readers interpret a pass without assuming it proves more than it does.
Standards and terminology to cite carefully
The ISTQB CTFL v4.0.1 syllabus is an introductory, teachable taxonomy. The ISO/IEC/IEEE 29119 series provides a standards framework: the ISO overview describes Part 1 as concepts, Part 2 as processes, Part 3 as documentation, and Part 4 as design techniques (series overview).
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Edition matters when referencing or purchasing a standard. IEC catalogs list ISO/IEC/IEEE 29119-1:2022 and Part 2:2021, newer editions than the 2013 versions sometimes shown in older catalog pages: Part 1 catalog entry and Part 2 catalog entry. Confirm the relevant part’s current edition for your use.
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