xUnit1003 Error

Theory methods must have test data

Cause

A Theory method does not have test data.

If a Theory method does not have test data, it is never run.

Add a data attribute such as InlineData, MemberData, or ClassData to the test method.
Change [Theory] to [Fact] if you want a non-parameterized test.

using Xunit;

public class xUnit1003
{
    [Theory]
    public void TestMethod(int _) { }
}

using Xunit;

public class xUnit1003
{
    [Fact]
    public void TestMethod() { }
}

using Xunit;

public class xUnit1003
{
    [Theory]
    [InlineData(5)]
    public void TestMethod(int _) { }
}