CODEWITHSUNDEEP
c#nunit
grokky
grokky

Reputation: 9295

NUnit constraint for delegate that does not throw a particular exception

I want to test that a delegate does not throw FooException, but I don't care if it throws anything else. Therefore I can't use the Nothing constraint.

The constraints model doesn't have something like this:

Assert.That(del, Throws.Not.InstanceOf<FooException>());   //can't use Not like this

Is that possible somehow?

Upvotes: 2

Views: 369

Answers (2)

Charlie
Charlie

Reputation: 13736

This is slightly awkward but should do it

Assert.That(Assert.Catch(del), Is.Null.Or.Not.TypeOf<FooException>());

Personally, I prefer the two-line version

var ex = Assert.Catch(del);
Assert.That(ex, Is.Null.Or.Not.TypeOf<FooException>());

or the even clearer three-liner

var ex = Assert.Catch(del);
if (ex != null)
    Assert.That(ex, Is.Not.TypeOf<FooException>());

This works because not asserting at all is the same as succeeding.

The lack of a more direct way to test this in the syntax reflects an opinion of the developers - at least at the time - that you should always know what exception you are expecting.

Upvotes: 3

Kote
Kote

Reputation: 2266

Looks like nunit does not provide it out of the box.
But you have some workarounds:
You may use additional assertion framework, like FluentAssertions, which allows you to do next assertion:

del.ShouldNotThrow<FooException>();

Also you can write your own custom-constraints, like ThrowsNothingConstraint

Or you can just write custom metod 

public void AssertException<T>(Action act) where T : Exception
{
    try
    {
        act();
    }
    catch (T e)
    {
        Assert.Fail();
    }
    catch (Exception e)
    {
        Assert.Pass();
    }
}

Upvotes: 3

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