Testing — General

Structure

• One test file per source module.
• Name tests as specifications: "should <behavior> when <condition>".
• Group related cases with describe/context blocks.
• Follow Arrange-Act-Assert (AAA), with a blank line between each phase.

What to Test

• Happy path: expected inputs produce expected outputs.
• Edge cases: empty input, zero, maximum values, boundary conditions.
• Error paths: invalid input, missing data, external failures.

Mocking

• Mock only what you don't control: HTTP calls, databases, filesystems, clocks.
• Never mock the unit under test.
• Restore mocks after each test to prevent state leakage.

Assertions

• Assert specific values, not just that something was called.
• On error paths, assert both the error type and message.
• Avoid assertions inside loops — use parameterized tests instead.

Coverage

• Focus on behavior coverage, not line coverage.
• 100% coverage does not mean a test suite is complete.
• Missing: edge cases, concurrent access, failure paths that coverage tools can't see.