tdd

name: tdd description: 'C# .NET Test-Driven Development workflow following Red-Green-Refactor with xUnit, NUnit, or MSTest. Use when writing new features or fixing bugs with tests first.'

TDD — Test-Driven Development for C#

Apply the Red-Green-Refactor cycle for all C# feature work.

Cycle

1. Red — Write a Failing Test

• Write a test that describes the desired behavior before any production code exists.
• Use the test framework already in the project (xUnit, NUnit, or MSTest).
• Test name: MethodName_Scenario_ExpectedBehavior (or WhenX_ThenY for BDD style).
• Run dotnet test and confirm the test fails for the right reason.

2. Green — Make It Pass

• Write the minimal production code to make the test pass.
• Do not over-engineer: only implement what the test requires.
• Run dotnet test and confirm the test now passes.
• Do not proceed until all tests pass.

3. Refactor — Improve Without Breaking

• Apply the refactor skill to improve structure, naming, and duplication.
• Run dotnet test after every change to confirm no regressions.
• Commit clean, passing code.

Rules

• One test per behavior.
• Tests must be independent and idempotent.
• No branching or conditionals inside tests.
• Follow the Arrange-Act-Assert (AAA) pattern.
• Mock only external dependencies; never mock code under test.

Test Frameworks

Validation

Run after each phase:

dotnet test

Or with coverage:

dotnet-coverage collect -f cobertura -o coverage.cobertura.xml dotnet test