Testing Levels: Unit to Acceptance

Unit Testing

Test the smallest piece (a method or class) in isolation, with dependencies mocked. Written by developers with JUnit/TestNG; runs in milliseconds on every commit.

Integration Testing

Test how modules work together: controller to service to repository, or your app to a payment gateway. Catches contract mismatches and wiring errors.

System Testing

Test the complete integrated system against the SRS in a production-like environment: end-to-end flows, browsers, data migrations.

Acceptance Testing

• UAT - business users validate real scenarios before sign-off.
• Alpha - tested in-house; Beta - tested by real users in the field.

Regression, Smoke, Sanity, End-to-End

• Regression - rerun old suites after any change; the backbone of CI.
• Smoke - quick critical-path check of a new build (login, home, checkout).
• Sanity - focused check that a specific fix works and did not break neighbours.
• End-to-End - full user journey across systems (browse, cart, pay, email, refund).

Key Points

• Test pyramid: many unit tests, fewer integration tests, few E2E tests.
• Each level has a different tester and a different question.
• Acceptance is owned by the business, not by QA.