# Asserting and comparing

> Perform assertions with constraints and compare the values of custom Unity types in your tests.

Unity Test Framework extends NUnit with Unity-specific custom APIs for comparing, asserting, and providing constraints for your assertions.

## Asserting

A test fails if Unity logs a message other than a regular log or warning message. You can use [`LogAssert`](https://docs.unity3d.com/Packages/com.unity.test-framework@latest/index.html?subfolder=/api/UnityEngine.TestTools.LogAssert.html) to check for an expected message in the log so the test doesn't fail when Unity logs the message.

Use `LogAssert.Expect` before running the code under test, as the check for expected logs runs at the end of each frame.

A test also reports a failure if an expected message does not appear, or if Unity does not log any regular log or warning messages.

The following example uses `LogAssert.Expect` to expect both a regular log message and an error message in the Editor log:

```lang-cs
[Test]
public void LogAssertExample()
{
    // Expect a regular log message
    LogAssert.Expect(LogType.Log, "Log message");
    
    // The test fails without the following expected log message     
    Debug.Log("Log message");
    
    // An error log
    Debug.LogError("Error message");
    
    // Without expecting an error log, the test would fail
    LogAssert.Expect(LogType.Error, "Error message");
}
```

### Asserting with constraints

NUnit allows you to write human-readable, descriptive [assertions](https://docs.nunit.org/articles/nunit/writing-tests/assertions/assertions.html) with the `Assert.That` mechanism, where the first parameter is an object under test and the second parameter describes conditions that the object has to meet.

Unity Test Framework extends this with a custom constraint type and declared an overlay [`Is`](https://docs.unity3d.com/Packages/com.unity.test-framework@latest/index.html?subfolder=/api/UnityEngine.TestTools.Constraints.Is.html) class. To resolve ambiguity between the original implementation and the custom one you must explicitly declare it with a `using` statement or via addressing through the full type name `UnityEngine.TestTools.Constraints.Is`.

## Comparing

Unity Test Framework provides custom equality comparers and utilities to enable easier verification of custom Unity type values in your tests. Comparable types include \[Color], \[Quaternion] and Vectors.

Use these classes to compare two objects of the same type for equality within the range of a given tolerance using [NUnit constraints](https://docs.nunit.org/articles/nunit/writing-tests/constraints/Constraints.html) or [Unity constraints](https://docs.unity3d.com/Packages/com.unity.test-framework@latest/index.html?subfolder=/api/UnityEngine.TestTools.Constraints.Is.html).

Call `Instance` to apply the default calculation error value to the comparison. To set a specific error value, instantiate a new comparer object using a one argument constructor `ctor(float error)`.

For the full list of available comparers and example usage, refer to the API reference for [`UnityEngine.TestTools.Utils`](https://docs.unity3d.com/Packages/com.unity.test-framework@latest/index.html?subfolder=/api/UnityEngine.TestTools.Utils.html).

## Additional resources

* [Arrange, act, assert](/engine/6000.7/manual/scripting/test-framework-introduction/overview/general-introduction/arrange-act-assert.md)
* [Asserting logs](/engine/6000.7/manual/scripting/test-framework-introduction/overview/general-introduction/asserting-logs.md)
* [Semantic test assertion](/engine/6000.7/manual/scripting/test-framework-introduction/overview/general-introduction/semantic-test-assertion.md)
* [Custom comparison](/engine/6000.7/manual/scripting/test-framework-introduction/overview/general-introduction/custom-comparison.md)