Tech Due Diligence CQ-2: Test Coverage and Testing Strategy

Write a testing strategy document that defines the team's approach at each level. Specify what should be unit tested (all business logic, utility functions, data transformations), what should be integration tested (API endpoints, database interactions, external service integrations), and what should be end-to-end tested (critical user journeys, payment flows, authentication). Set measurable coverage targets appropriate to the codebase. For backend business logic, aim for 80%+ line coverage. For critical financial or safety-related code, push for 90%+. For UI components, focus on testing behaviour rather than chasing high coverage numbers. Track coverage over time and require new code to meet the threshold. Make test execution a mandatory gate in CI/CD. Pull requests should not be mergeable if tests fail. Consider adding coverage regression checks that block merging if coverage drops below the baseline. Set up proper testing environments at each level: unit tests run in isolation with mocked dependencies, integration tests use test databases and service stubs, and end-to-end tests run against a staging environment that mirrors production. Focus on test quality during code reviews. Good tests verify meaningful behaviour rather than implementation details, use clear assertions that communicate intent, follow naming conventions that describe the scenario, avoid excessive mocking that makes tests brittle, and are deterministic with no flaky behaviour. Track test reliability as an operational concern. Flaky tests erode confidence in the suite and lead developers to ignore failures. Maintain a flaky test dashboard and quarantine or fix unreliable tests promptly. Consider specialised testing approaches where they add value: property-based testing for complex algorithms, snapshot testing for UI components, contract testing for microservice APIs, and chaos engineering for resilience testing.