False positive on RSPEC-2201

[martin...@codestudio.com]

So I have a C# unit test that looks like this:

        [Fact]
        public void MyTest()
        {
            // Arrange.
            var classUnderTest = new MyClass();

            // Act.            
            Action action = () =>
            {
                classUnderTest.MyMethod(null).ToList();
            };

            // Assert.
            action.Should()
                .Throw<ArgumentNullException>();
        }

I'm getting the error on the ToList() call. The error given is 'S2201 Use the return value of method 'ToList', which has no side effect.' However ToList does have a side effect. In this instance MyMethod(null) is a method that returns IEnumerable<T> and has a yield return within it. It will throw an argument null exception as null is passed in, however it only does this if the returned IEnumerable<T> is iterated over. As such the side effect that ToList has is to cause the IEnumerable<T> to be iterated. I get the same result with .Any(). However I want to use .List() in other tests as I want to ensure that MyMethod picks up things if the collection that is passed to it has duff data in the middle of it.

https://rules.sonarsource.com/csharp/RSPEC-2201

[Amaury Leve]

Hi Martin,

This is indeed a False Positive although we have been working on a new rule that might be interesting for you in this situation (https://github.com/SonarSource/sonar-csharp/issues/1165). As you can see it is recommended to split yield methods into 2 parts and doing so you won't need this call to ToList() to actually check the ArgumentNullException being thrown.

Cheers,

Amaury

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Amaury Levé | SonarSource

Software Developer - .Net Team

http://sonarsource.com

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