csharp-nunit

NUnit Best Practices

Your goal is to help me write effective unit tests with NUnit, covering both standard and data-driven testing approaches.

Project Setup

• Use a separate test project with naming convention [ProjectName].Tests
• Reference Microsoft.NET.Test.Sdk, NUnit, and NUnit3TestAdapter packages
• Pin package versions explicitly in your .csproj and commit packages.lock.json for reproducible, supply-chain-safe builds (e.g., dotnet add package NUnit --version <version>)
• Create test classes that match the classes being tested (e.g., CalculatorTests for Calculator)
• Use .NET SDK test commands: dotnet test for running tests

Test Structure

• Apply [TestFixture] attribute to test classes
• Use [Test] attribute for test methods
• Follow the Arrange-Act-Assert (AAA) pattern
• Name tests using the pattern MethodName_Scenario_ExpectedBehavior
• Use [SetUp] and [TearDown] for per-test setup and teardown
• Use [OneTimeSetUp] and [OneTimeTearDown] for per-class setup and teardown
• Use [SetUpFixture] for assembly-level setup and teardown

Standard Tests

• Keep tests focused on a single behavior
• Avoid testing multiple behaviors in one test method
• Use clear assertions that express intent
• Include only the assertions needed to verify the test case
• Make tests independent and idempotent (can run in any order)
• Avoid test interdependencies

Data-Driven Tests

• Use [TestCase] for inline test data
• Use [TestCaseSource] for programmatically generated test data
• Use [Values] for simple parameter combinations
• Use [ValueSource] for property or method-based data sources
• Use [Random] for random numeric test values
• Use [Range] for sequential numeric test values
• Use [Combinatorial] or [Pairwise] for combining multiple parameters

Assertions

• Use Assert.That with constraint model (preferred NUnit style)
• Use constraints like Is.EqualTo, Is.SameAs, Contains.Item
• Use Assert.AreEqual for simple value equality (classic style)
• Use CollectionAssert for collection comparisons
• Use StringAssert for string-specific assertions
• Use Assert.Throws<T> or Assert.ThrowsAsync<T> to test exceptions
• Use descriptive messages in assertions for clarity on failure

Mocking and Isolation

• Consider using Moq or NSubstitute alongside NUnit
• Mock dependencies to isolate units under test
• Use interfaces to facilitate mocking
• Consider using a DI container for complex test setups

Test Organization

• Group tests by feature or component
• Use categories with [Category("CategoryName")]
• Avoid [Order] unless absolutely necessary (e.g., integration tests with unavoidable shared state); prefer making each test fully independent to uphold idempotency
• Use [Author("DeveloperName")] to indicate ownership
• Use [Description] to provide additional test information
• Consider [Explicit] for tests that shouldn't run automatically
• Use [Ignore("Reason")] to temporarily skip tests