Is That String Null, Empty, Or WhiteSpace?

When dealing with string data, you will almost certainly encounter a situation where you must determine if your string has a value.

Having a value means it is NOT one of the following:

1. null
2. Empty String: string.Empty or ""
3. Whitespace (tab, space, newlines, etc)

You would be surprised how these innocuous concepts can land you in trouble with unintentional bugs.

Let us start by creating a xUnit test project.

dotnet new xunit -o EmptyStringTests

We then add Shouldly to help with our assertions now that FluentAssertions has a ridiculous license.

dotnet add package Shouldly

Next, we write a small method to supply our test data cases. This will save us from copying and pasting the test cases repeatedly.

public static IEnumerable<object[]> SampleStrings()
{
  yield return [null]; // a null
  yield return [""]; // a null string
  yield return [" "]; // a space
  yield return ["   "]; // a tab
  yield return [Environment.NewLine]; // a newline
}

Next, we will create tests for several methodologies of testing for the absence of data:

1. Comparing against null
2. Comparing against string.Empty
3. Using the method string.IsNullOrEmpty
4. Using the method IsNullOrWhiteSpace
5. Trim the string and checking its length is zero

The code for the tests is as follows:

[Theory]
[MemberData(nameof(SampleStrings))]
public void NullCheck(string sample)
{
    (sample == null).ShouldBe(true);
}


[Theory]
[MemberData(nameof(SampleStrings))]
public void NullStringCheck(string sample)
{
    (sample == "").ShouldBe(true);
}

[Theory]
[MemberData(nameof(SampleStrings))]
public void IsNullOrEmpty(string sample)
{
    string.IsNullOrEmpty(sample).ShouldBe(true);
}

[Theory]
[MemberData(nameof(SampleStrings))]
public void IsNullOrWhiteSpace(string sample)
{
    string.IsNullOrWhiteSpace(sample).ShouldBe(true);
}

[Theory]
[MemberData(nameof(SampleStrings))]
public void TrimCheck(string sample)
{
    (sample?.Trim().Length == 0).ShouldBe(true);
}

If we run our unit tests, the results are surprising.

Only one technique - using the method string.IsNullOrWhiteSpace passes all the tests.

TLDR

Use the method string.IsNullOrWhiteSpace to reliably check if a string has data.

The code is in my GitHub.

Happy hacking!