UnityTest attribute

UnityTest attribute is the main addition to the standard NUnit library for the Unity Test Framework. This type of unit test allows you to skip a frame from within a test (so background tasks can finish) or give certain commands to the Unity Editor, such as performing a domain reload or entering Play Mode from an Edit Mode test.

In Play Mode, the UnityTest attribute runs as a coroutine. Whereas Edit Mode tests run in the EditorApplication.update callback loop.

The UnityTest attribute is, in fact, an alternative to the NUnit Test attribute, which allows yielding instructions back to the framework. Once the instruction is complete, the test run continues. If you yield return null, you skip a frame. That might be necessary to ensure that some changes do happen on the next iteration of either the EditorApplication.update loop or the game loop.

Edit Mode example

The most simple example of an Edit Mode test could be the one that yields null to skip the current frame and then continues to run:

[UnityTest]
public IEnumerator EditorUtility_WhenExecuted_ReturnsSuccess()
{
    var utility = RunEditorUtilityInTheBackground();

    while (utility.isRunning)
    {
        yield return null;
    }

    Assert.IsTrue(utility.isSuccess);
}

Play Mode example

In Play Mode, a test runs as a coroutine attached to a MonoBehaviour. So all the yield instructions available in coroutines, are also available in your test.

From a Play Mode test you can use one of Unity’s Yield Instructions:

WaitForFixedUpdate: to ensure changes expected within the next cycle of physics calculations.
WaitForSeconds: if you want to pause your test coroutine for a fixed amount of time. Be careful about creating long-running tests.

The simplest example is to yield to WaitForFixedUpdate:

[UnityTest]
public IEnumerator GameObject_WithRigidBody_WillBeAffectedByPhysics()
{
    var go = new GameObject();
    go.AddComponent<Rigidbody>();
    var originalPosition = go.transform.position.y;

    yield return new WaitForFixedUpdate();

    Assert.AreNotEqual(originalPosition, go.transform.position.y);
}