FAI xUnit Test

Objective

Create maintainable .NET tests that balance speed, isolation, and behavioral confidence.

Patterns

Step 1 - Unit Test Example

public class PriceServiceTests
{
    [Theory]
    [InlineData(1000, 0.10, 900)]
    [InlineData(2000, 0.25, 1500)]
    public void ApplyDiscount_ReturnsExpectedValue(decimal amount, decimal rate, decimal expected)
    {
        var service = new PriceService();
        var result = service.ApplyDiscount(amount, rate);
        Assert.Equal(expected, result);
    }
}

Step 2 - Mock External Dependencies

var repository = new Mock<IOrderRepository>();
repository.Setup(r => r.GetByIdAsync("A1")).ReturnsAsync(new Order("A1"));

Step 3 - Integration Test with WebApplicationFactory

public class OrdersApiTests : IClassFixture<WebApplicationFactory<Program>>
{
    private readonly HttpClient _client;

    public OrdersApiTests(WebApplicationFactory<Program> factory)
    {
        _client = factory.CreateClient();
    }

    [Fact]
    public async Task GetOrder_Returns200()
    {
        var response = await _client.GetAsync("/api/orders/A1");
        Assert.Equal(HttpStatusCode.OK, response.StatusCode);
    }
}

Step 4 - Test Quality Rules

• Prefer behavior assertions over implementation details.
• Avoid sleeps; use deterministic clocks/fakes.
• Isolate test data; no cross-test leakage.
• Keep test names scenario-oriented.

Validation Checklist

Troubleshooting

Advanced Implementation Notes

Operational Guardrails

• Define measurable SLOs before rollout.
• Capture baseline metrics and compare deltas post-change.
• Add alert thresholds with explicit on-call ownership.
• Use environment-specific overrides for dev/staging/prod.

CI/CD and Validation Expansion

# Example verification sequence
npm run lint
npm test
npm run build

{
  "quality_gate": {
    "required": true,
    "min_score": 0.8,
    "block_on_failure": true
  }
}

Security and Compliance Checks

Performance and Cost Notes

• Budget requests and tokens per endpoint/class of workload.
• Profile p95 and p99 latency as separate objectives.
• Add caching only where correctness is preserved.
• Use periodic reports to catch drift in cost/quality.

Extended Troubleshooting