---

name: test-driven-development description: Use when implementing any feature or bugfix in C#/.NET before writing implementation code; applies to gRPC services, EF Core data access, and Blazor components

Test-Driven Development (TDD)

Overview

Write the test first. Watch it fail. Write minimal code to pass.

Core principle: If you didn't watch the test fail, you don't know if it tests the right thing.

Violating the letter of the rules is violating the spirit of the rules.

When to Use

Always:

• New features
• Bug fixes
• Refactoring
• Behavior changes

Exceptions (ask your human partner):

• Throwaway prototypes
• Generated code
• Configuration files

Thinking "skip TDD just this once"? Stop. That's rationalization.

The Iron Law

CopyNO PRODUCTION CODE WITHOUT A FAILING TEST FIRST

Write code before the test? Delete it. Start over.

No exceptions:

• Don't keep it as "reference"
• Don't "adapt" it while writing tests
• Don't look at it
• Delete means delete

Implement fresh from tests. Period.

Red-Green-Refactor

Copydigraph tdd_cycle {
    rankdir=LR;
    red [label="RED\nWrite failing test", shape=box, style=filled, fillcolor="#ffcccc"];
    verify_red [label="Verify fails\ncorrectly", shape=diamond];
    green [label="GREEN\nMinimal code", shape=box, style=filled, fillcolor="#ccffcc"];
    verify_green [label="Verify passes\nAll green", shape=diamond];
    refactor [label="REFACTOR\nClean up", shape=box, style=filled, fillcolor="#ccccff"];
    next [label="Next", shape=ellipse];

    red -> verify_red;
    verify_red -> green [label="yes"];
    verify_red -> red [label="wrong\nfailure"];
    green -> verify_green;
    verify_green -> refactor [label="yes"];
    verify_green -> green [label="no"];
    refactor -> verify_green [label="stay\ngreen"];
    verify_green -> next;
    next -> red;
}

RED - Write Failing Test

Write one minimal test showing what should happen.

Copyusing var context = new EctDbContext(options);
context.Workflows.Add(new Workflow { Id = "WF-123", Name = "Test" });
await context.SaveChangesAsync();

var dataService = new WorkflowDataService(context);
var service = new WorkflowServiceImpl(dataService);
var mockContext = new Mock<ServerCallContext>();

// Act
var result = await service.GetWorkflow(
    new GetWorkflowRequest { WorkflowId = "WF-123" }, 
    mockContext.Object
);

// Assert
Assert.NotNull(result);
Assert.Equal("WF-123", result.WorkflowId);
Assert.Equal("Test", result.Name);

}

// ✅ ECTSystem Pattern: Test exception handling in gRPC service [Fact] public async Task GetWorkflow_WithNullId_ThrowsRpcExceptionWithInvalidArgument() { // Arrange var mockDataService = new Mock(); var service = new WorkflowServiceImpl(mockDataService.Object); var mockContext = new Mock();

Copy// Act & Assert
var exception = await Assert.ThrowsAsync<RpcException>(async () =>
    await service.GetWorkflow(new GetWorkflowRequest { WorkflowId = "" }, mockContext.Object)
);

Assert.Equal(StatusCode.InvalidArgument, exception.Status.StatusCode);

}

// ✅ ECTSystem Pattern: Test EF Core data access with InMemory database [Fact] public async Task CreateWorkflow_WithValidData_PersistsToDatabase() { // Arrange var options = new DbContextOptionsBuilder() .UseInMemoryDatabase("create-test") .Options;

Copyusing (var context = new EctDbContext(options))
{
    var dataService = new WorkflowDataService(context);
    var workflow = new Workflow { Id = "WF-NEW", Name = "New Workflow" };

    // Act
    await dataService.CreateWorkflowAsync(workflow);

    // Assert - Verify database state changed
    var created = await context.Workflows.FindAsync("WF-NEW");
    Assert.NotNull(created);
    Assert.Equal("New Workflow", created.Name);
}

}

// ✅ ECTSystem Pattern: Test Blazor component event handling [Fact] public async Task WorkflowComponent_OnApproveClick_CallsApproveService() { // Arrange var mockWorkflowClient = new Mock(); mockWorkflowClient.Setup(c => c.ApproveWorkflowAsync(It.IsAny())) .ReturnsAsync(true);

Copyvar component = new WorkflowApprovalComponent 
{ 
    WorkflowClient = mockWorkflowClient.Object,
    WorkflowId = "WF-123"
};

// Act
await component.OnApproveClickAsync();

// Assert
mockWorkflowClient.Verify(c => c.ApproveWorkflowAsync("WF-123"), Times.Once);
Assert.True(component.IsApproved);

}

Copy
**Clear xUnit names, AAA pattern, tests real behavior (InMemory DB), gRPC exceptions with status codes, service layer mocking only when necessary**
</Good>

<Bad>
```csharp
// ❌ Vague test name, unclear what behavior it tests
[Fact]
public async Task RetryWorks()
{
    var mock = new Mock<IOperation>();
    mock.SetupSequence(m => m.ExecuteAsync())
        .ThrowsAsync(new InvalidOperationException())
        .ThrowsAsync(new InvalidOperationException())
        .ReturnsAsync("success");
    await RetryHelper.RetryOperationAsync(mock.Object.ExecuteAsync);
    mock.Verify(m => m.ExecuteAsync(), Times.Exactly(3));
}

// ❌ Tests mock behavior not actual WorkflowService behavior
[Fact]
public async Task GetWorkflow_ReturnsData()
{
    var mockDataService = new Mock<IWorkflowDataService>();
    mockDataService.Setup(s => s.GetWorkflowByIdAsync(It.IsAny<string>()))
        .ReturnsAsync(new Workflow { Id = "123", Name = "Test" });
    
    var service = new WorkflowServiceImpl(mockDataService.Object);
    var result = await service.GetWorkflow(new GetWorkflowRequest { WorkflowId = "123" }, null);
    
    Assert.Equal("123", result.WorkflowId);  // Testing mock, not real behavior
}

Vague name, tests mock not code, doesn't test actual EF Core queries or gRPC response mapping

Requirements:

• One behavior
• Clear xUnit naming: MethodUnderTest_Scenario_ExpectedResult
• Real code (no mocks unless unavoidable)
• AAA pattern: Arrange, Act, Assert

Verify RED - Watch It Fail

MANDATORY. Never skip.

Copy# Run specific test in ECTSystem
dotnet test AF.ECT.Tests --filter "FullyQualifiedName~RetryOperation_RetriesFailedOperations_SucceedsAfterThirdAttempt" --no-build

# Or run all tests to see the failure
dotnet test AF.ECT.Tests --no-build

Confirm:

• Test fails (not build errors)
• Failure message shows expected vs actual
• Fails because feature missing (not compilation errors)
• For gRPC: Assert.ThrowsAsync shows status code or response mismatch
• For EF Core: InMemoryDatabase reflects test data changes

Test passes? You're testing existing behavior. Fix test.

Test errors? Fix compilation errors (check namespaces, using statements), re-run until it fails correctly.

GREEN - Minimal Code

Write simplest code to pass the test.

Don't add features, refactor other code, or "improve" beyond the test.

Verify GREEN - Watch It Pass

MANDATORY.

Copy# Run all tests in ECTSystem
dotnet test AF.ECT.Tests --no-build

# Or run specific test
dotnet test AF.ECT.Tests --filter "FullyQualifiedName~RetryOperation_RetriesFailedOperations_SucceedsAfterThirdAttempt" --no-build

# Verify no warnings introduced
dotnet build ElectronicCaseTracking.sln /p:TreatWarningsAsErrors=true

Confirm:

• Test passes
• Other tests still pass
• Build output: 0 errors, 0 warnings
• gRPC call returns expected response or correct exception
• No CS* compiler warnings

Test fails? Fix code, not test.

Other tests fail? Fix now.

Build warnings? Fix warnings - don't suppress them.

REFACTOR - Clean Up

After green only:

• Remove duplication
• Improve names
• Extract helpers

Keep tests green. Don't add behavior.

Repeat

Next failing test for next feature.

Good Tests

Why Order Matters

"I'll write tests after to verify it works"

Tests written after code pass immediately. Passing immediately proves nothing:

• Might test wrong thing
• Might test implementation, not behavior
• Might miss edge cases you forgot
• You never saw it catch the bug

Test-first forces you to see the test fail, proving it actually tests something.

"I already manually tested all the edge cases"

Manual testing is ad-hoc. You think you tested everything but:

• No record of what you tested
• Can't re-run when code changes
• Easy to forget cases under pressure
• "It worked when I tried it" ≠ comprehensive

Automated tests are systematic. They run the same way every time.

"Deleting X hours of work is wasteful"

Sunk cost fallacy. The time is already gone. Your choice now:

• Delete and rewrite with TDD (X more hours, high confidence)
• Keep it and add tests after (30 min, low confidence, likely bugs)

The "waste" is keeping code you can't trust. Working code without real tests is technical debt.

"TDD is dogmatic, being pragmatic means adapting"

TDD IS pragmatic:

• Finds bugs before commit (faster than debugging after)
• Prevents regressions (tests catch breaks immediately)
• Documents behavior (tests show how to use code)
• Enables refactoring (change freely, tests catch breaks)

"Pragmatic" shortcuts = debugging in production = slower.

"Tests after achieve the same goals - it's spirit not ritual"

No. Tests-after answer "What does this do?" Tests-first answer "What should this do?"

Tests-after are biased by your implementation. You test what you built, not what's required. You verify remembered edge cases, not discovered ones.

Tests-first force edge case discovery before implementing. Tests-after verify you remembered everything (you didn't).

30 minutes of tests after ≠ TDD. You get coverage, lose proof tests work.

Common Rationalizations

Red Flags - STOP and Start Over

• Code before test
• Test after implementation
• Test passes immediately
• Can't explain why test failed
• Tests added "later"
• Rationalizing "just this once"
• "I already manually tested it"
• "Tests after achieve the same purpose"
• "It's about spirit not ritual"
• "Keep as reference" or "adapt existing code"
• "Already spent X hours, deleting is wasteful"
• "TDD is dogmatic, I'm being pragmatic"
• "This is different because..."

All of these mean: Delete code. Start over with TDD.

Example: Bug Fix

Bug: WorkflowService accepts null workflow ID in gRPC call

RED

Copy[Fact]
public async Task GetWorkflow_WithNullId_ThrowsInvalidArgument()
{
    var mockContext = new Mock<ServerCallContext>();
    var mockDataService = new Mock<IDataService>();
    var service = new WorkflowServiceImpl(mockDataService.Object);
    
    await Assert.ThrowsAsync<RpcException>(async () =>
        await service.GetWorkflow(new GetWorkflowRequest { WorkflowId = "" }, mockContext.Object)
    );
}

Verify RED

Copy$ dotnet test AF.ECT.Tests --filter "GetWorkflow_WithNullId" --no-build
FAIL: Expected RpcException not thrown

GREEN (in AF.ECT.Server/Services/WorkflowServiceImpl.cs)

Copypublic override async Task<GetWorkflowResponse> GetWorkflow(
    GetWorkflowRequest request, ServerCallContext context)
{
    if (string.IsNullOrWhiteSpace(request.WorkflowId))
        throw new RpcException(new Status(StatusCode.InvalidArgument, "Workflow ID required"));
    
    var workflow = await _dataService.GetWorkflowByIdAsync(request.WorkflowId);
    return new GetWorkflowResponse { WorkflowId = workflow.Id };
}

Verify GREEN

Copy$ dotnet test AF.ECT.Tests --filter "GetWorkflow_WithNullId" --no-build
PASS: 1 passed

REFACTOR Consider extracting validation to separate validator method for reuse across gRPC methods.

Verification Checklist

Before marking work complete:

• Every new public method has a test (gRPC services, data service methods, validators)
• Watched each test fail before implementing (RED phase verified)
• Each test failed for expected reason (feature missing, not build errors)
• Wrote minimal code to pass each test
• dotnet test AF.ECT.Tests --no-build shows all pass
• dotnet build ElectronicCaseTracking.sln succeeds with 0 errors/warnings
• Tests use real code, real DbContext with InMemory (Moq only if unavoidable)
• Edge cases and exceptions covered (invalid input, null refs, RpcExceptions)
• Test names follow xUnit pattern: MethodUnderTest_Scenario_ExpectedResult
• For gRPC methods: test both success path and exception paths with correct StatusCode
• For EF Core: test with InMemoryDatabase, not mocks
• For Blazor components: test with JSRuntime mock, verify UI state changes
• No compiler warnings introduced (CS* errors)
• Audit logging interceptor called for applicable methods

Can't check all boxes? You skipped TDD. Start over.

When Stuck

Debugging Integration

Bug found? Write failing test reproducing it. Follow TDD cycle. Test proves fix and prevents regression.

Never fix bugs without a test.

Testing Anti-Patterns

When adding mocks or test utilities, read @testing-anti-patterns.md to avoid common pitfalls:

• Testing mock behavior instead of real behavior
• Adding test-only methods to production classes
• Mocking without understanding dependencies

Final Rule

CopyProduction code → test exists and failed first
Otherwise → not TDD

No exceptions without your human partner's permission.