Black box testing

You test the system by inputs/outputs without knowing internal code.

Examples:

• UI testing
• API testing
• acceptance tests

White box testing

You test with knowledge of internal implementation.

Examples:

• unit tests
• branch/condition coverage
• code-level edge cases

Grey box testing

You have partial knowledge of internals.

Examples:

• API tests with DB knowledge
• testing with logs/metrics

Diagram

  graph LR
A[Black box\n(No internals)] --> B[Grey box\n(Some internals)] --> C[White box\n(Full internals)]

When to use what

• Black box: verify user-visible behavior
• White box: verify correctness and edge cases
• Grey box: efficient end-to-end checks