Types of testing: Unit, integration, system, load and acceptance test

In short: Tests are distinguished by scope and goal: from the single building block through interplay to the whole system, load and release by the customer.

In more detail: Errors are cheaper the earlier they are found. So testing is done in levels. Names differ slightly by source, the idea is the same.

In Depth

By scope

• Unit test: single functions or classes, fast, many of them.
• Integration test: interplay of several modules or with database, API, file system.
• System test: the whole system against requirements, in an environment like production.
• Acceptance test (UAT): the customer checks whether the system meets their requirements, basis of acceptance.
• End-to-end test: complete user journey through the interface, for example with Playwright.

By goal

• Functional test: does it do the right thing?
• Regression test: does the old still work after a change?
• Load test / stress test: how does the system behave with many users? (tools: k6, JMeter, Locust)
• Performance test: response times and throughput.
• Security test: vulnerabilities, penetration test.
• Usability test: is it understandable?
• Compatibility test: different browsers, devices, versions.
• Smoke test: quick basic check after deployment.

By method

Black box (only inputs and outputs, without code), white box (with knowledge of the structure, coverage), grey box. Manual or automated. Test cases consist of precondition, input, expected result. Equivalence classes and boundary value analysis reduce the number of necessary cases.

Practice

Plan testing from the start, document test cases and results (important for IHK documentation), automate the repeatable ones in the CI pipeline, and keep the test pyramid in mind: many fast unit tests, fewer integration tests, few E2E tests. A passed test never proves freedom from errors, only the absence of certain errors.

See also: Unit test, Black-box testing, White-box testing, Test pyramid, Acceptance and handover, CI/CD pipeline