Testing Exception Messages with Shouldly

Question

Is there a way to test the exception messages with shouldly?

An example:

public class MyException: Exception{
}

The method to be tested:

public class ClassUnderTest
{
    public void DoSomething() 
    {
        throw new MyException("Message");
    }
}

I would usually test this in this way:

[TestMethod]
public void Test()
{
    try
    {
        new ClassUnderTest().DoSomething();
        Assert.Fail("Exception not thrown");
    } catch(MyException me)
    {
        Assert.AreEqual("Message", me.Message);
    }catch(Exception e)
       Assert.Fail("Wrong exception thrown");
    }
}

With shouldly I can now test if a exception is thrown:

[TestMethod]
public void TestWithShouldly()
{
    Should.ThrowException<MyException>(() => new ClassUnderTest().DoSomething());
}

But how can I test the message of the exception?

score 97 · Accepted Answer · edited Dec 07 '20 at 06:26

97

The Should.Throw() method returns the exception, so you can continue to test if for other things.

For example:

Should.Throw<MyException>(() => new ClassUnderTest().DoSomething())
    .Message.ShouldBe("My Custom Message");

Or, if you want to do more than just test the message:

MyException ex = Should.Throw<MyException>(() => new ClassUnderTest().DoSomething());

You can then do what you like with ex.

Note: Shouldly V2 uses Should.ThrowException<>()

edited Dec 07 '20 at 06:26

Matthew Lock

13,144
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answered Nov 11 '16 at 09:43

Colin Mackay

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Damn, so simple. Should have figured it out myself. Thank you – Steffen Nov 11 '16 at 09:53
17

Apparently, in latest versions it should be `Throw` – Noctis Oct 03 '17 at 16:17
What do you do if your Action takes a ref and can't be used in a lambda? > Cannot use ref local inside an anonymous method, lambda expression, or query expression – Steve Jun 21 '23 at 19:12

Testing Exception Messages with Shouldly

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