C# – Using ClassInitialize in a test class

When you want to initialize something for all unit tests in a test class, you can apply the ClassInitialize attribute to a method. This initialization method only runs once and is ran before any of the unit tests. Here’s an example of how to add ClassInitialize:

using Microsoft.VisualStudio.TestTools.UnitTesting;

[TestClass()]
public class CalculatorTests
{
	[ClassInitialize]
	public static void TestClassInit(TestContext context)
	{
		//Initialize something for all tests
	}

	[ClassCleanup]
	public static void TestClassCleanup()
	{
		//The opposite of ClassInitialize
	}

	[TestMethod]
	public void SomeTest()
	{
		//test here
	}
}
Code language: C# (cs)

Note: ClassCleanup is the opposite of ClassInitialize. It runs once after all the tests have finished running.

ClassInitialize method requirements

You can only use ClassInitialize on a method with a very specific signature, otherwise it results in a runtime error and the tests won’t run. In the Test Runner, the tests will appear in a Not Run state (with a blue icon). You can look in the Output > Tests window and see following error:

Method TestClassInit has wrong signature. The method must be static, public, does not return a value and should take a single parameter of type TestContext. Additionally, if you are using async-await in method then return-type must be Task.

The solution is to change the method to meet ClassInitialize’s requirements: public static void with a single TestContext parameter, like this:

[ClassInitialize]
public static void TestClassInit(TestContext context)
{
	//Initialize something for all tests
}
Code language: C# (cs)

After you fix the method signature, the tests will run.