Correctly testing that a method does nothing under certain cicrumstances

user_15960052 0
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I am running into a little trouble with my unit testing code and SonarQube.

I have the following simple test:

    [TestMethod]
    public void TestFormat_Null()
    {
        _sut.Format(null);
    }

    public void Format(IPhone phoneNumber)
    {
        if (phoneNumber == null) return;
        FormatNumber(phoneNumber);
        FormatAreaCode(phoneNumber);
        FormatCountryCode(phoneNumber);
    }

The requirement here is, that if null is passed in, the method will simply do nothing, since there is nothing to format and also not crash with an exception.

Now the problem we are getting is that our SonarQube complains, that this is a test without any Assertions.

Is there any better way to declare a test that tests for a method not doing anything or is this a case where the SonarQube warning should simply be ignored?

sonarqube mstest unit-testing c#
2 Answers

I found the solution within FluentAssertions.

My new code wraps the old call to the _sut in an action and uses Fluent Assertions Should Not Throw mechanism.

This is an elegant solution because we were using FluentAssertions already anyway. I was just never aware of the Should Not Throw assertion it offers. I only ever knew about Should Throw until now.

user_159600520

A test that doesn't fail (and isn't inconclusive) is a test that passes.

Some testing libraries like NUnit include "Assert.DoesNotThrow", others don't such as MsTest and xUnit. Technically there's already an implicit Assert.DoesNotThrow at the end of every single test.

I would recommend that you consider what is being tested here. If you pass null then what should happen to the SUT? Does it set some property as null or maybe an empty string, and who uses that property? Surely Format() does something!

So if we test pure functions by looking a their return values, we can test void methods by looking at what they actually do -- their side-effects.

[TestMethod]
public void TestFormat_Null()
{
    _sut.Format(null);
    Assert.equal(string.empty, _sut.PrintInputText())
}

That might prove a more valuable test, better than a workaround like Assert.True(true)... and maybe justify how SonarCube's warning may still hold useful after all.

user_2838790
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