How to use ApprovalTests with xUnit's Theory attribute

Problem

In ApprovalTests, the Namer generates a unique name for each approved/received file. This filename takes the format of {ClassName}.{MethodName}.approved.txt.

This works perfectly for Fact based tests. But, if you are writing a Theory based test the filename will not be unique as a theory-based test is data-driven and therefore has multiple calls to the same method.

Example

Let’s look at an example

public class TestClass { [InlineData(true)] [InlineData(false)] [Theory] public void Test(bool flag) { var result = TestThisMethod(flag); Approvals.Verify(result); } } 

In the above snippet, the filename generated for both the tests will be TestClass.Test.approved.txt. This means that you have only 1 approval file for both the tests.

Solution

The naming pattern of the default namer is*{ClassName}.{MethodName}.{AdditionalInformation(optional)}.approved.{Extension}*. So, we can leverage the_AdditionalInformation_ part to generate unique filenames for our tests.

public class TestClass { [InlineData(true)] [InlineData(false)] [Theory] public void Test(bool flag) { NamerFactory.AdditionalInformation = $"Flag-{flag}"; var result = TestThisMethod(flag); Approvals.Verify(result); } } 

Now, when we run the tests, 2 files will be generated

• TestClass.Test.Flag-true.approved.txt
• TestClass.Test.Flag-false.approved.txt

Note: We can pass any information to the AdditionalInformation property as long as it is unique between tests.