Testing Patterns

Overview

Tests ensure code correctness and enable confident refactoring. Follow these patterns for consistent, maintainable tests.

Test Framework Stack

•xUnit - Test framework
•Moq - Mocking library
•FluentAssertions - Readable assertions

Test Structure

Arrange-Act-Assert (AAA)

Every test follows this pattern:

csharp

[Fact]
public async Task GetByIdAsync_WithValidId_ReturnsTask()
{
    // Arrange
    var taskId = Guid.NewGuid();
    var expectedTask = new TaskItem { Id = taskId, Title = "Test Task" };
    _repositoryMock.Setup(r => r.GetByIdAsync(taskId, It.IsAny<CancellationToken>()))
        .ReturnsAsync(expectedTask);

    // Act
    var result = await _sut.GetByIdAsync(taskId);

    // Assert
    result.Should().NotBeNull();
    result!.Id.Should().Be(taskId);
    result.Title.Should().Be("Test Task");
}

Test Class Structure

csharp

public class TaskServiceTests
{
    private readonly Mock<ITaskRepository> _repositoryMock;
    private readonly Mock<ILogger<TaskService>> _loggerMock;
    private readonly TaskService _sut; // System Under Test

    public TaskServiceTests()
    {
        _repositoryMock = new Mock<ITaskRepository>();
        _loggerMock = new Mock<ILogger<TaskService>>();
        _sut = new TaskService(_repositoryMock.Object, _loggerMock.Object);
    }

    // Tests...
}

Naming Conventions

Test Method Names

Format: MethodName_Scenario_ExpectedResult

csharp

// Good - descriptive names
public async Task GetByIdAsync_WithValidId_ReturnsTask()
public async Task GetByIdAsync_WithNonExistentId_ReturnsNull()
public async Task CreateAsync_WithValidRequest_CreatesAndReturnsTask()
public async Task DeleteAsync_WithExistingId_ReturnsTrue()

// Bad - unclear names
public async Task TestGet()
public async Task Test1()

Mocking with Moq

Setup Mock Returns

csharp

// Return a value
_repositoryMock.Setup(r => r.GetByIdAsync(taskId, It.IsAny<CancellationToken>()))
    .ReturnsAsync(expectedTask);

// Return null
_repositoryMock.Setup(r => r.GetByIdAsync(It.IsAny<Guid>(), It.IsAny<CancellationToken>()))
    .ReturnsAsync((TaskItem?)null);

Verify Mock Calls

csharp

_repositoryMock.Verify(r => r.CreateAsync(It.IsAny<TaskItem>(), It.IsAny<CancellationToken>()), Times.Once);
_repositoryMock.Verify(r => r.DeleteAsync(taskId, It.IsAny<CancellationToken>()), Times.Once);

FluentAssertions

Basic Assertions

csharp

result.Should().Be(expected);
result.Should().BeNull();
result.Should().NotBeNull();
items.Should().HaveCount(3);
items.Should().BeEmpty();
result.IsCompleted.Should().BeTrue();

Edge Case Coverage

Always Test These Scenarios

•GET: found, not found, empty list
•CREATE: success, validates input, sets defaults
•UPDATE: success, not found, partial update
•DELETE: success, not found