What is a happy path test vs an edge case test?
Answer
A happy path test tests the expected, normal flow — the scenario where everything goes right, inputs are valid, and the system returns the expected successful result. Example: test that a valid user login succeeds. Edge case tests test boundary conditions and unusual inputs that might reveal bugs: (1) Boundary values: minimum/maximum valid values, values just inside/outside boundaries (0, -1, 1, Integer.MAX_VALUE). (2) Empty/null inputs: empty string, null, empty array. (3) Large inputs: very long strings, large arrays. (4) Invalid types: wrong format dates, negative quantities. (5) Concurrent access: multiple simultaneous requests. (6) Failure scenarios: network timeout, database unavailable. Common bugs hide in edge cases. The happy path test is necessary but not sufficient — a comprehensive test suite tests both happy paths and the most important edge cases. The equivalence class partitioning technique identifies representative edge cases systematically.