Testing Test Writing

@grimmolf/mga-soap-calculator-testing-test-writing

Follow TDD cycle (RED-GREEN-REFACTOR) writing failing tests first, covering edge cases and error states, using explicit fixtures, and maintaining fast test suites with coverage gates. Use this skill when writing unit tests, integration tests, contract tests, or any test code in test files. Applies to test directories, spec files, test runners (Jest, Vitest, pytest), mocking strategies, regression prevention, and ensuring statement/branch coverage thresholds that block merges when dropped.