Guided test-driven development workflow for .NET 10 using xUnit v3, WebApplicationFactory, Testcontainers, and Verify snapshots. Follows the strict red-green-refactor cycle. Use when: "TDD", "test-driven", "let's TDD this", "red green refactor", "write the test first", or when building a feature wit

/tdd Red Green Refactor for .NET What Guides a strict test driven development cycle for .NET features. Instead of writing implementation first and bolting on tests after, this command flips the order: write a failing test that defines the desired behavior, implement the minimum code to make it pass, then refactor with confidence. Every cycle uses the .NET testing stack: xUnit v3 Test framework with [Fact] and [Theory] WebApplicationFactory Integration tests against the real HTTP pipeline Testcontainers Real databases (PostgreSQL, SQL Server) in tests Verify Snapshot testing for complex response structures FakeTimeProvider Deterministic time in tests When User says "TDD", "test driven", "let's TDD this", "write the test first" Building a new feature with clear acceptance criteria Fixing a bug (write a test that reproduces the bug first, then fix) Adding behavior to an existing feature (test the new behavior first) Any time the user wants proof that code works before it ships Skip TDD for: Trivial config changes, scaffolding without logic, documentation. How Cycle: Red Green Refactor Each feature goes through one or more TDD cycles. A cycle covers one discrete behavior. Step 1: Red Write the Failing Test Write a test that describes the desired behavior. The test MUST fail because the implementation does not exist yet. Run the test and confirm it fails: If the test passes without implementation, the test is not testing what you think. Rewrite it. Step 2: Green Minimal Implementation Write the minimum code to make the test pass. Do not add features, optimizations, or edge case handling. The goal is a green test, nothing more. Create the endpoint, handler, request/response types, and EF config as needed Use the simplest logic that satisfies the test assertion Do not refactor yet ugly passing code is fine at this stage Run the test and confirm it passes: Step 3: Refactor Clean Up with Confidence Now that the test is green, refactor freely: Extract methods, rename variables, improve structure Apply modern C patterns (primary constructors, records, collection expressions) Add validation, error handling, and edge cases (with new tests for each) Run the full test suite after each refactor step to catch regressions If any test goes red during refactoring, undo the last change and try a smaller step. Multi Cycle Features Most features require multiple TDD cycles. Plan the cycles upfront: Each cycle adds one behavior. Never combine multiple behaviors in a single cycle. Test Infrastructure Setup If the project lacks test infrastructure, set it up before the first cycle: 1. Create test project with xUnit v3 and required packages 2. Configure WebApplicationFactory with Testcontainers for the real database 3. Add a shared fixture to avoid spinning up containers per test class 4. Verify the infrastructure with a simple health check test Example Related /verify Run full verification after completing all TDD cycles /scaffold Generate initial feature structure that tests will drive