Any way to ignore Possible Null Reference Exception warnings when using Assert statements?

Question

I do not want to disable the warnings completely, just when it's in an Assert statement.

So for example if I have the following two lines

var someObject = GetObject();
Assert.IsNotNull(someObject, "someObject should not be null");
Assert.AreEqual(expectedValue, someObject.SomeProperty);

I'll get the possible null reference warning on the second line on someObject.SomeProperty. Is it possible to disable the warning when it is within a certain call, like Assert.AreEqual?

Since this is an issue with a lot of unit tests, I don't want to litter the tests with the ReSharper disable code.

Right now the only option I can think of is to change every Assert.IsNotNull call to be

var someObject = GetObject();
if(someObject == null)
{
  Assert.Fail("someObject is null");
  return;
}

Although this kind of seems to defeat the purpose of having Assert.IsNotNull in the first place. Just wondering if there is a better way.

Knotting

Related: #4393956 – Halliday

Can you post a fuller example? I cannot reproduce this; when using NUnit's assertion library the addition of Assert.IsNotNull removes the warning - and whether it is in a test or not has no effect. – Rebecarebecca

@JamesWorld, I'm using MBUnit, not sure if that makes a difference. The code I posted does give the warning using MBUnit 2.4.2 and ReSharper 6.1. I know it doesn't matter if it's in a test or not, but I'm only concerned with disabling it in test classes. Everywhere else it should be enabled. – Knotting

Yes I spotted the use of MBUnit, that's why I called out I was using NUnit. I switch my test to MBUnit and see that is doesn't remove the warning. The problem must lie in differences in their implementation. – Rebecarebecca

Answer 1

I don't know the specific library you use, but I'd try something like

Assert.IsTrue(someObject != null);

or, for the sake of completeness,

Assert.IsNotNull(someObject, "someObject must not be null");
Assert.IsNotNull(someObject.SomeProperty, "SomeProperty must not be null either");
Assert.SomethingElse(...);

Composer

Thanks for the answer, but the issue will still exist. Even if I assert the object and the property is not null, the warnings don't care and give the warning anyways. The warnings will only go away if I do a object == null and return out of the method. – Knotting

@Knotting Out of curiosity, despite the warnings, do the tests pass and fail as you would expect ? – Composer

yes. This is more of a nitpicky issue. I just don't like the solution wide inspections being filled with a bunch of warnings that shouldn't actually be warnings. This doesn't affect the actual code or the testing or anything. – Knotting

@Knotting Oh my, I get it now, they come from ReSharper not from the compiler ... My bad. That dumb thing should provide facilities to instruct it to shut up, but I never used it so I'm afraid I can't provide further advice. They aren't real warnings anyway (they don't come from the compiler, am I correct ?), so I'd probably just end up ignoring them in your situation....but I'm very lazy when it comes to best practices... – Composer

Answer 2

Add this to your project:

public static class AssertionsExtensions
{
    [NotNull]
    public static TSubject ShouldNotBeNull<TSubject>([CanBeNull] this TSubject source,
        [CanBeNull] string because = "", [CanBeNull] [ItemCanBeNull] params object[] reasonArgs)
    {
        source.Should().NotBeNull(because, reasonArgs);

        // ReSharper disable once AssignNullToNotNullAttribute
        return source;
    }
}

Then use it like this, for example:

            // Assert
            succeeded.Should().Be(true, "<USB loopback cable must be connected and COM port must be correct.>");
            DeviceStatus deviceStatusNotNull = testRunner.Result.ShouldNotBeNull();
            deviceStatusNotNull.DeviceAddress.Should().Be(deviceAddress);
            deviceStatusNotNull.IsInNetwork.Should().Be(true);

Dioptric

Answer 3

If I am not mistaken, your problem is that resharper gives warnings when null is not checked foreach object. You can modify resharper rules not to give null warnings in test classes. Here is a link about changing ReSharper naming style for test methods.

Perjury

You know you program too much when you start writing for each as one word. :) Could you provide the steps as to how to do this? How do I tell Resharper what to consider a test class? – Knotting

@Knotting you made me smile:) please have a look; atombrenner.blogspot.com/2010/07/… – Perjury

-1 I think you are mistaken. The appearance of the warning is not specific to test classes. – Rebecarebecca

@JamesWorld the appearance of the warning is not specific to test classes, you are right, but what Brandon needs is to disable the warnings only in test classes if I am not wrong. – Perjury

Disabling warnings en masse is never a good idea - this would hide warnings of genuine concern. – Rebecarebecca

@JamesWorld, daryal is correct. I want to have the warnings enabled except for in test classes. – Knotting

Still not a good idea... much better to solve the issue properly or specifically disable the warnings if you really can't find a way. – Rebecarebecca

@JamesWorld, I don't quite understand the objection. Assert.IsNotNull is solving the issue properly. If it does come up as null the test will fail and the method will stop executing. The only issue is the warning that I haven't checked for nulls, when I have. Also, @daryal, that only applies to naming inspections, not anything else including exceptions. – Knotting

The objection is that if you subsequently add faulty logic to your tests that would have been caught by a warning, then you won't see it. – Rebecarebecca

@Knotting you should find the null warning in the list and modify it as the page suggests. (In the resharper options find the rule related to the null and continue with what is suggested in the page). – Perjury

What would be nice is if R# noticed the check for null in Assert.IsNotNull, rather than looking for other types of null checks. – Ulrich

Answer 4

Use NUnit instead of MBUnit. NUnit's implementation of Assert.IsNotNull() is picked up as guaranteeing not null whereas MBUnit's is not.

Rebecarebecca

How to guaranteee for Assert.That(result, Is.Not.Null) ? – Cuttlebone

Answer 5

You can use R# external annotations to suppress the warnings (see http://grahamrhay.wordpress.com/2011/01/09/external-annotations/).

What version of MbUnit/Gallio are you using?

Austen

Answer 6

You can use ContractAnnotations to indicate the execution stops if parameter is null. See jetbrains contract annotations. Sample class:

 public static class FluentExtensions
 {
        //see: https://www.jetbrains.com/help/resharper/2017.3/Contract_Annotations.html
        [ContractAnnotation("null => stop")]
        public static void ShouldNotBeNull(this object objToTest)
        {
            objToTest.Should().NotBeNull();
        }   

 }

Usage:

doc.ShouldNotBeNull();
doc.Content.ShouldNotBeNull();

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