Test if a class has an attribute?

Question

I'm trying to do a little Test-First development, and I'm trying to verify that my classes are marked with an attribute:

[SubControllerActionToViewDataAttribute]
public class ScheduleController : Controller

How do I unit test that the class has that attribute assigned to it?

score 158 · Accepted Answer · answered Aug 04 '09 at 07:47

158

check that

Attribute.GetCustomAttribute(typeof(ScheduleController),
    typeof(SubControllerActionToViewDataAttribute))

isn't null (Assert.IsNotNull or similar)

(the reason I use this rather than IsDefined is that most times I want to validate some properties of the attribute too....)

answered Aug 04 '09 at 07:47

Marc Gravell

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to only check if the attribute is present, which is usually all that is needed for parameterless/propertyless attributes, it's cheaper to use .IsDefined, as it will query the metadata, and not deserialize and instantiate the attribute object. – Lasse V. Karlsen Aug 04 '09 at 07:52
1

As is the point about IsDefined being cheaper... but in most cases (and in particular unit tests) you are unlikely to notice the difference. Maybe if it was a tight loop in production code... – Marc Gravell Aug 04 '09 at 07:58
@Marc- I agree about that the difference in performance would probably not be noticeable in a unit test. I'd get the attribute if I needed to use it, which as you say is the scenario in most cases. I recently used IsDefined in a framework I was writing to exclude a column in a dropdown of sortable fields- this worked well as I didn't need to use to the attribute itself. – RichardOD Aug 04 '09 at 08:01
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How can we test the same for a method? – Manvinder Singh Apr 23 '20 at 11:20

RichardOD · Answer 2 · 2012-06-23T16:04:42.690

96

The same you would normally check for an attribute on a class.

Here's some sample code.

typeof(ScheduleController)
.IsDefined(typeof(SubControllerActionToViewDataAttribute), false);

I think in many cases testing for the existence of an attribute in a unit test is wrong. As I've not used MVC contrib's sub controller functionality I can't comment whether it is appropriate in this case though.

edited Jun 23 '12 at 16:04

answered Aug 04 '09 at 07:47

RichardOD

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Did +1 and then noticed error. It should be .IsDefined(typeof(Type), false); – Alexander Beletsky Apr 05 '12 at 13:13
@alexanderb you are of course right. I've updated my answer now. I must of not checked my answer against the compiler at the time! Thanks for pointing out the error – RichardOD Jun 23 '12 at 16:05
10

this approach is faster then previous – Slava Jul 18 '14 at 12:11

score 23 · Answer 3 · answered Mar 12 '16 at 19:19

23

It is also possible to use generics on this:

var type = typeof(SomeType);
var attribute = type.GetCustomAttribute<SomeAttribute>();

This way you do not need another typeof(...), which can make the code cleaner.

answered Mar 12 '16 at 19:19

This company is turning evil.

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This does not work for me. Which `using` .. am I missing? – Apr 19 '17 at 13:22
@Scanzy I'm not sure, are you not using a IDE? (Usually they suggest the correct `using`) What error do you get? – This company is turning evil. Apr 19 '17 at 13:23
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ok, [here](https://msdn.microsoft.com/it-it/library/hh194292(v=vs.110).aspx) I found the `GetCustomAttribute` method is avaliable from .NET 4.5 and my IDE was set to 3.5 so everything is clear now – Apr 19 '17 at 16:35

score 13 · Answer 4 · answered Sep 25 '15 at 11:23

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I know this thread is really old, but if somebody stumble upon on it you may find fluentassertions project very convenient for doing this kind of assertions.

typeof(MyPresentationModel).Should().BeDecoratedWith<SomeAttribute>();

answered Sep 25 '15 at 11:23

Aleksey L.

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Test if a class has an attribute?

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