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testland/dotnet-unit-tests

Use whenever the task is to write, add, fix or review .NET unit tests in C#, F# or VB.NET, even a quick test for one method: xUnit.net by default, plus NUnit and MSTest. Covers Fact and Theory tables, fixtures, mocking, FluentAssertions, async tests and coverage with dotnet test.

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NUnit - attribute-driven .NET testing (reference)

Companion reference for dotnet-unit-tests. Consult for existing NUnit codebases, teams preferring constraint-model assertions, or legacy .NET Framework 4.x targets. For brand-new .NET code, xUnit (SKILL.md) is the more mainstream default.

Per docs.nunit.org:

NUnit's distinguishing properties vs xUnit: annotation-driven lifecycle, constraint-model assertions (Assert.That(actual, Is.EqualTo(expected))), and multiple parametrize attributes ([TestCase], [Values], [Random], [Range]).

Install and first test

dotnet new nunit -n MyTests
# Or: dotnet add package NUnit + NUnit3TestAdapter + Microsoft.NET.Test.Sdk

using NUnit.Framework;

[TestFixture]
public class CalculatorTests
{
    [Test]
    public void Adds_TwoNumbers()
    {
        Assert.That(Calculator.Add(1, 2), Is.EqualTo(3));
    }
}

[TestFixture] is optional in NUnit 3+ (classes with [Test] methods are auto-discovered) - pick a convention and document it. Run: dotnet test.

Parametrize

[Test]
[TestCase(1, 2, 3)]
[TestCase(0, 0, 0)]
[TestCase(-1, 1, 0)]
public void Adds_VariousInputs(int a, int b, int expected)
{
    Assert.That(Calculator.Add(a, b), Is.EqualTo(expected));
}

// Combinatorial: 3 × 2 = 6 runs
[Test]
public void Adds_FromValues([Values(1, 2, 3)] int a, [Values(0, 1)] int b)
{
    Assert.That(Calculator.Add(a, b), Is.EqualTo(a + b));
}

[Test]
public void Adds_Range([Range(0, 10, 2)] int n)   // n = 0, 2, 4, 6, 8, 10
{
    Assert.That(Calculator.Add(n, n), Is.EqualTo(n * 2));
}

// Method-source
[Test]
[TestCaseSource(nameof(AddCases))]
public void Adds_FromSource(int a, int b, int expected) { ... }

public static IEnumerable<TestCaseData> AddCases()
{
    yield return new TestCaseData(1, 2, 3);
    yield return new TestCaseData(0, 0, 0);
}

[Random(0, 100, 5)] generates random values - pin a seed ([Random(seed: 42, ...)]) for CI reproducibility.

Constraint-model assertions

Per nu-docs - the constraint model composes (Is.Not.Null.And.Not.Empty) and produces detailed failure messages; classic Assert.AreEqual / Assert.IsTrue still work but are discouraged in NUnit 3+:

Assert.That(value, Is.EqualTo(expected));
Assert.That(value, Is.Not.EqualTo(expected));
Assert.That(value, Is.GreaterThan(0));
Assert.That(s, Does.Contain("substring"));
Assert.That(s, Does.Match("regex"));
Assert.That(list, Has.Count.EqualTo(3));
Assert.That(list, Has.Member("alice"));
Assert.That(list, Is.Ordered);
Assert.That(list, Has.All.GreaterThan(0));
Assert.That(opt, Is.Null);
Assert.That(value, Is.InstanceOf<MyClass>());
Assert.That(action, Throws.TypeOf<ArgumentException>());
Assert.That(actual, Is.EqualTo(0.0).Within(0.001));   // float tolerance

Lifecycle

[OneTimeSetUp] / [OneTimeTearDown] (once per fixture) and [SetUp] / [TearDown] (per test).

Categories and parameterized fixtures

[Test]
[Category("Integration")]
public void IntegrationTest() { }
// Filter: dotnet test --filter Category=Integration

[TestFixture("postgres")]
[TestFixture("mysql")]
public class DatabaseTests
{
    private string _engine;
    public DatabaseTests(string engine) { _engine = engine; }

    [Test]
    public void Connect() { /* runs against postgres AND mysql */ }
}

CI

Same shape as xUnit: dotnet test --logger "trx;LogFileName=test-results.trx" --collect:"XPlat Code Coverage".

Anti-patterns

Anti-pattern	Why it fails	Fix
Classic `Assert.AreEqual` style	Discouraged in NUnit 3+	Constraint model `Assert.That(...)`
Unseeded `[Random]`	Non-deterministic CI runs	`[Random(seed: 42, ...)]`
Mix NUnit + xUnit in one solution	Two runners	Pick one

Limitations

Constraint model has a learning curve vs Assert.Equal() simplicity.
Parallelism is less aggressive than xUnit's parallel-by-default.

References

nu-docs - NUnit documentation
docs.nunit.org/articles/nunit/writing-tests/assertions/assertion-models/constraint.html - constraint model

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