Black Box, White Box and Test Design Techniques

Black Box Testing

Test behaviour without seeing code: give inputs, check outputs. Techniques below are all black box.

White Box Testing

Test with code knowledge: statement, branch and path coverage. Used in unit testing and code reviews.

Gray Box Testing

Partial knowledge: test APIs and database states while treating UI as a black box. Typical for QA engineers.

Equivalence Partitioning

Divide inputs into valid/invalid groups and test one value per group. Age 18-60: test 25 (valid), 10 and 70 (invalid).

Boundary Value Analysis

Bugs live at edges: for range 18-60 test 17, 18, 19, 59, 60, 61.

Decision Table Testing

Map combinations of conditions to actions. Login with valid/invalid username x valid/invalid password gives 4 rules and expected messages.

State Transition Testing

Test valid and invalid moves between states: order New to Paid to Shipped; Paid back to New must be rejected.

Use Case, Error Guessing, Pairwise

• Use case testing - walk the actor steps end to end.
• Error guessing - use experience: empty fields, special characters, huge files.
• Pairwise - cover all pairs of parameter values with few cases (browser x OS x role).

Key Points

• Black box needs no code; white box needs coverage tools.
• Boundaries plus partitions catch most input bugs.
• Combine techniques: partitions select values, tables cover logic.