SetUp

SetUpAttribute marks a method NUnit calls immediately before each [Test], [TestCase], [Theory], etc. in the fixture. Use it to reset or prepare per-test instance state that should not leak between cases.

The method lives on your TestFixture (or fixture base classes in the inheritance chain). Typical use is alongside TearDown for symmetrical cleanup afterward.

Normally you scatter multiple [SetUp] methods across inheritance levels (base, then derived). Declaring several marked methods on one class is allowed, but mutual order among them is undefined unless you constrain them logically.

Static and instance methods

SetUp may be static or an instance method. Instance methods execute on context.TestObject, meaning the same fixture instance that receives the imminent test (LifeCycle.SingleInstance) or a freshly constructed instance before every test when LifeCycle.InstancePerTestCase is in effect.

Prefer instance SetUp for fields on the test object; use static only when the preparation truly applies without a specific instance (be careful with shared static state under parallel runs).

Methods may be async (Task / Task<T>); NUnit awaits them like other async test infrastructure.

Failures and assumptions

If SetUp throws or an assertion fails, the test method body is not run; the result reflects a setup failure (FailureSite.SetUp). TearDown for that same per-test scope still runs afterwards in normal operation so you can release partially initialized resources—unless the run is aborted before teardown is reached.

If you use Assume.That(...) in SetUp, a failed assumption also prevents the test body from running (treated like a setup outcome). Teardown behavior matches the normal path above.

Usage

This is a parameterless attribute that can only be applied to methods.

[SetUp]

Applies To

Lifecycle Methods	Test Methods	Test Fixtures (Classes)	Assembly
✅	❌	❌	❌

Example

[SetUp]
public void Init()
{
    _counter = 0;
}

[Test]
public void TestMethod()
{
    _counter++;
    Assert.That(_counter, Is.EqualTo(1));
}

Inheritance

The SetUp attribute is inherited from any base class. Therefore, if a base class has defined a SetUp method, that method will be called before each test method in the derived class.

You may define a SetUp method in the base class and another in the derived class. NUnit will call base class SetUp methods before those in the derived classes.

Warning

If a base class SetUp method is overridden in the derived class, NUnit will not call the base class SetUp method; NUnit does not anticipate usage that includes hiding the base method. Note that you may have a different name for each method; as long as both have the [SetUp] attribute present, each will be called in the correct order.

Notes

TestContext — SetUp runs in per-test context; most TestContext APIs reflect the about-to-run test.
Multiple SetUp methods on the same declaration have no guaranteed relative order.
Base-class SetUp runs before derived-class SetUp (see Inheritance).