Unit test exception messages with xUnit

Question

I'm currently converting my MsTest unit tests to xUnit. With xUnit, is there a way to test exception messages? Is it correct to test exception messages as opposed just the exception type?

the_joric · Accepted Answer · 2017-05-30T08:58:38.087

137

I think it is correct to test for both Exception type and message. And both are easy in xUnit:

var exception = Assert.Throws<AuthenticationException>(() => DoSomething());
Assert.Equal(message, exception.Message);

edited May 30 '17 at 08:58

answered May 18 '11 at 10:11

the_joric

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@CsabaToth No you need Assert.ThrowsAsync<> to do this – jfmg Jan 18 '16 at 12:53
I'm sure I'm missing the obvious, but what is the `message` argument in the first line for? – Mark Embling Apr 28 '17 at 13:08
@MarkEmbling thanks for pointing that out -- it was probably a typo. I updated the answer. – the_joric May 30 '17 at 08:58

score 9 · Answer 2 · answered Nov 29 '16 at 23:42

9

Better to use the Record.Exception method as it matches the AAA pattern:

    [Fact]
    public void Divide_TwoNumbers_ExpectException()
    {
        var sut = new Calculator();
        var exception = Record.Exception(() => sut.Divide(10, 0));
        Assert.IsType(typeof(DivideByZeroException), exception);
    }

Hope this helps ...

answered Nov 29 '16 at 23:42

user1829319

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xUnit2007: Do not use typeof(System.DivideByZeroException) expression to check the type. Instead you can use: Assert.IsType(exception) – ggeorge Nov 28 '20 at 12:18

user2982369 · Answer 3 · 2017-09-06T13:15:53.693

2

Something like this

 var ex = Record.Exception(() => DoSomeThing());
 Assert.IsType(typeof(ArgumentNullException), ex);
 Assert.True(ex.Message.Contains("Your exception message"));

edited Sep 06 '17 at 13:15

answered Aug 25 '17 at 23:47

user2982369

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score 1 · Answer 4 · answered Jan 25 '18 at 17:36

1

BTW, Resharper prefers not to use typeof and suggests Assert.IsType instead, e.g.

var ex = Record.Exception(() => new FooController(null, null));
Assert.IsType<ArgumentNullException>(ex);

answered Jan 25 '18 at 17:36

Andy Creigh

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score 1 · Answer 5 · answered Mar 21 '11 at 10:59

xUnit uses Assert.Throws to test for exception types. You could catch the exception and Assert against the message if you needed. I think in general you want to test that the expected exception is thrown, and the exact message is really not necessary.

Assert.Throws<ArgumentNullException>()

The exception might be if you have a custom exception you are unit testing and you want to make sure the message generated is what you expect. Or if there are two ways that the same exception type can be thrown but with different messages, then asserting against the message would be valuable

`Throws()` returns Exception -- no need to catch it. – the_joric May 11 '12 at 11:59 — the_joric, May 11 '12 at 11:59

score 0 · Answer 6 · answered Mar 21 '11 at 10:57

An exception is no different than any other expected result of your test. It is natural to test that the message is the correct one as two different messages can come in the same exception type. However - I personally don't think of it as mandatory, at least not in all exceptions.

In our project each application exception also has a 'Message' object attached to it, so we verify the MessageId only, we don't verify that the message arguments are correct or the message's text. E.g if the message text is "Wrong parameter <{0}> was provided", we don't check that the argument that was passed to format {0} is as expected - this is not the intent. The message has a unique id - so we verify that the MessageID on the exception is 'WRONG_PARAMETER_PROVIDED'.

score 0 · Answer 7 · answered May 20 '20 at 07:36

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In the light of async stuff, new version would be

var ex = await Record.ExceptionAsync(() => myMethod(myParams));
Assert.IsType<SomeException>(ex);
Assert.Equal("My text of the error.", ex.Message);

answered May 20 '20 at 07:36

Nico Degraef

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score -1 · Answer 8 · answered Mar 28 '13 at 17:17

-1

xUnit website also mentions "Record.Exception" construct.

answered Mar 28 '13 at 17:17

Csaba Toth

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Unit test exception messages with xUnit

8 Answers8