csharp-testing-standards

C# Testing Standards

Description

Defines the testing standards, patterns, and conventions for all C# unit and integration test projects. Rules cover test framework usage, naming, structure, mocking, assertions, and parameterization. Apply these rules uniformly across all test projects.

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1. Framework & Tooling

• Test framework: NUnit 3
• Mocking: Moq
• Coverage: coverlet.collector
• Test runner: Microsoft.NET.Test.Sdk + NUnit3TestAdapter

Core NUnit attributes in use:

Attribute	Purpose
[TestFixture]	Marks the test class
[Test]	Marks a single test method
[SetUp]	Runs before each test
[TearDown]	Runs after each test
[OneTimeSetUp]	Runs once before all tests in the fixture
[TestCase]	Parameterized test inline values

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2. Test Class Structure

2.1 Visibility

Test classes are internal. They do not need to be public – NUnit discovers them via the test runner regardless.

[TestFixture]
internal class OrderServiceTests { }

2.2 System Under Test Field

Name the field under test _sut (system under test) and initialize it in [SetUp]:

private OrderService _sut = null!;

2.3 Mock Fields

Declare all mocks as class-level fields initialized in [SetUp]:

private Mock<IOrderRepository> _orderRepositoryMock = null!;
private Mock<ILogger<OrderService>> _loggerMock = null!;

2.4 SetUp Method

• Initialize all mocks and the SUT in the [SetUp] method.
• Configure happy-path default behaviors here so individual tests only override what they specifically need.
• Keep [SetUp] focused – it should not contain assertions or complex logic.

[SetUp]
public void Setup()
{
    _orderRepositoryMock = new Mock<IOrderRepository>();
    _orderRepositoryMock
        .Setup(r => r.GetByIdAsync(It.IsAny<Guid>(), It.IsAny<CancellationToken>()))
        .ReturnsAsync((Order?)null);

    _sut = new OrderService(
        _orderRepositoryMock.Object,
        NullLogger<OrderService>.Instance);
}