C_SHARP_SKILLS/.ai/skills/05-functions-debugging-testing.md

Skill 05 - Functions, Debugging, and Testing

Function Design

• Follow DRY, but do not abstract too early.
• Keep functions small enough to explain in one sentence.
• Prefer pure functions for business rules when possible.
• Make side effects obvious in names and placement.
• Use parameters for required input and return values for computed output.
• Use tuples for small local groupings; use named types for public APIs or durable concepts.

Async Rules

• Use Task/Task<T> for asynchronous operations.
• Suffix asynchronous methods with Async.
• Pass CancellationToken through I/O or long-running operations.
• Never use .Result or .Wait() in request-handling or UI code.

Debugging Rules

• Reproduce the issue first.
• Use breakpoints, watches, locals, call stack, and trace/log output.
• Verify assumptions with tests rather than comments alone.
• Remove temporary diagnostic output before final code unless it becomes structured logging.

Unit Testing Rules

• Use Arrange, Act, Assert.
• Test normal, boundary, invalid, and null cases.
• Unit-test pure logic without external services.
• Integration-test database, filesystem, HTTP, serialization, and DI wiring.
• Keep tests deterministic. Avoid reliance on local time, random values, order, or environment unless controlled.

Common Commands

dotnet test
dotnet test --filter FullyQualifiedName~SomeTestName
dotnet test --collect:"XPlat Code Coverage"