Quote:
Is there any other way to test that method without writing any extra code
As a matter of fact, your methods and all the C# code are "tested" by the compiler for certain things, and the most important one being type safety. Try updating the method to:
private static string MethodToTest() {
}
And you will see that certain "tests" will not pass. For more advanced tests, try using an inheritance construct with your Program type, and see what the compiler says.
As for logical tests (
for what goes inside the method), that is not something that your compiler understands. For that, you need to write custom tests where you tell the testing suite how to verify that the program works as expected.