How do I use Assert Throws to assert the type of the exception

Question

How do I use Assert Throws to assert the type of the exception and the actual message wording  Something like this  Assert Throws lt Exception gt           gt user MakeUserActive    WithMessage  quot Actual exception message quot    The method I am testing throws multiple messages of the same type  with different messages  and I need a way to test that the correct message is thrown depending on the context

User · Accepted Answer

Assert Throws returns the exception that s thrown which lets you assert on the exception   var ex   Assert Throws lt Exception gt       gt  user MakeUserActive     Assert That ex Message  Is EqualTo  Actual exception message       So if no exception is thrown  or an exception of the wrong type is thrown  the first Assert Throws assertion will fail  However if an exception of the correct type is thrown then you can now assert on the actual exception that you ve saved in the variable   By using this pattern you can assert on other things than the exception message  e g  in the case of ArgumentException and derivatives  you can assert that the parameter name is correct   var ex   Assert Throws lt ArgumentNullException gt       gt  foo Bar null    Assert That ex ParamName  Is EqualTo  bar       You can also use the fluent API for doing these asserts   Assert That      gt  foo Bar null    Throws Exception    TypeOf lt ArgumentNullException gt       With Property  ParamName      EqualTo  bar       or alternatively  Assert That      Assert Throws lt ArgumentNullException gt       gt          foo Bar null       ParamName  Is EqualTo  bar       A little tip when asserting on exception messages is to decorate the test method with the SetCultureAttribute to make sure that the thrown message is using the expected culture  This comes into play if you store your exception messages as resources to allow for localization

User · Answer

Assert That myTestDelegate  Throws ArgumentException      With Property  Message   EqualTo  your argument is invalid

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Since I m disturbed by the verbosity of some of the new NUnit patterns  I use something like this to create code that is cleaner for me personally   public void AssertBusinessRuleException TestDelegate code  string expectedMessage        var ex   Assert Throws lt BusinessRuleException gt  code       Assert AreEqual ex Message  expectedMessage      public void AssertException lt T gt  TestDelegate code  string expectedMessage  where T Exception       var ex   Assert Throws lt T gt  code       Assert AreEqual ex Message  expectedMessage       The usage is then   AssertBusinessRuleException      gt  user MakeUserActive     Actual exception message

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I recently ran into the same thing  and suggest this function for MSTest  public bool AssertThrows Action action  where T   Exception       try  action      catch Exception exception        if  exception GetType      typeof T           return true        return false     Usage  Assert IsTrue AssertThrows lt FormatException gt  delegate  newMyMethod MyParameter         There is more in Assert that a particular exception has occured  Assert Throws in MSTest

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You can now use the ExpectedException attributes  e g    Test   ExpectedException typeof InvalidOperationException     ExpectedMessage  You can t do that    public void MethodA WithNull ThrowsInvalidOperationException         MethodA null

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A solution that actually works  public void Test         throw new MyCustomException  quot You can t do that  quot        TestMethod  public void ThisWillPassIfExceptionThrown         var exception   Assert ThrowsException lt MyCustomException gt                gt  Test             quot This should have thrown  quot        Assert AreEqual  quot You can t do that  quot   exception Message      This works with using Microsoft VisualStudio TestTools UnitTesting

User · Answer

To expand on persistent s answer  and to provide more of the functionality of NUnit  you can do this  public bool AssertThrows lt TException gt       Action action      Func lt TException  bool gt  exceptionCondition   null      where TException   Exception       try               action              catch  TException ex                if  exceptionCondition    null                        return exceptionCondition ex                     return true            catch               return false             return false     Examples     No exception thrown - test fails  Assert IsTrue      AssertThrows lt InvalidOperationException gt                gt            Wrong exception thrown - test fails  Assert IsTrue      AssertThrows lt InvalidOperationException gt                gt    throw new ApplicationException             Correct exception thrown - test passes  Assert IsTrue      AssertThrows lt InvalidOperationException gt                gt    throw new InvalidOperationException             Correct exception thrown  but wrong message - test fails  Assert IsTrue      AssertThrows lt InvalidOperationException gt                gt    throw new InvalidOperationException  quot ABCD quot               ex   gt  ex Message     quot 1234 quot         Correct exception thrown  with correct message - test passes  Assert IsTrue      AssertThrows lt InvalidOperationException gt                gt    throw new InvalidOperationException  quot 1234 quot               ex   gt  ex Message     quot 1234 quot

[c#] How do I use Assert.Throws to assert the type of the exception?

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