How do you Unit TEst code which uses String.IsNullOrEmpty?

Question

Do you write two Unit Tests? One for value being Null and one for value being string.Empty? The similar for string.IsNullOrWhiteSpace()?

Answer 1

Yes, you would typically want to test that all possible classes of inputs (null, empty, whitespace, non-whitespace) get the right outputs.

That means testing both alternatives for String.IsNullOrEmpty() and all three alternatives for String.IsNullOrWhitespace().

Answer 2

Typically I'd use NUnit test cases to test these permutations. They'll give you coverage of the three different checks without duplicating your test code.

For example:

[TestCase("")]
[TestCase(null)]
public class SomeTest(string stringValue)
{
   Assert.Throws<ArgumentException>(()=> CheckIfNullOrEmpty(stringValue));
}

public void CheckIfNullOrEmpty(string val)
{
   if(string.IsNullOrEmpty(val))
   {
       throw new ArgumentException();
   }
}