Should a method should be throwing an exception to the Unit Test? - visual-studio-2010

Question

I have a simple method for sending emails:
public void notifyEmail(string messageSubject, string messageBody)
{
MailMessage message = new MailMessage(from, to);
message.Subject = messageSubject;
message.Body = messageBody;
SmtpClient client = new SmtpClient(smtp_client);
client.Send(message);
message.Dispose();//release everything related
}
And a unit test (I'm learning):
[TestMethod()]
public void notifyEmailTest()
{
eMail target = new eMail("TEST Subject","TEST Body"); // TODO: Initialize to an appropriate value
bool testSent = true;
try
{
target.notifyEmail();
}
catch (Exception)
{
testSent = false;
}
Assert.IsTrue(testSent);
}
I deliberately set the smtp_client variable value to something invalid.
Running the code in my project results in an error.
Running the test method results in a Pass. Should my test or method be structured differently so that errors will fail the test?

Answer 1

I always do everything I can to avoid putting try-catch clauses on my unit tests. Instead try using the ExpectedException attribute (the attribute is the same for NUnit and MSTest) and set the type to the exception you are expecting i.e.
[TestMethod]
[ExpectedException(typeof(NetworkException))]
public void ShouldThrowNetworkExceptionIfSmtpServerIsInvalid)
{
//... test code here.
}
Another approach that I have used is to create a static class with an AssertExpectedException method since sometimes a method can throw the same type of exception for different reasons and the only way to know for sure if the accurate message is being returned is with custom code since the attribute does not assert the message the thrown exception is returning.
Hope this helps.
Regards.

Answer 2

If you expect that target.notifyEmail() should be throwing an exception, then that's what you should be testing for. If you were using NUnit you could use Assert.Throws<T>, e.g.
[Test]
public void notifyEmailTestFails()
{
// TODO: Initialize to an appropriate value
eMail target = new eMail("TEST Subject","TEST Body");
Assert.Throws<InvalidOperationException>(target.notifyEmail());
}
However, now I see you're using VSUnit you should be using [ExpectedException(typeof(...))]
as mentioned in other answers.
In general you should have separate tests for success, failure, and for exception conditions.

Answer 3

The way I normally do this is to decorate the test with ExpectedException (
http://msdn.microsoft.com/en-us/library/microsoft.visualstudio.testtools.unittesting.expectedexceptionattribute(v=vs.80).aspx)
. But you want to catch something MUCH less generic than "Exception."
If you don't want to use expected exception, then instead of:
bool testSent = true;
try
{
target.notifyEmail();
}
catch (Exception)
{
testSent = false;
}
Assert.IsTrue(testSent);
You can be a little less verbose:
try{
target.notifyEmail();
Assert.Fail("Expected an exception here");
}
catch (SmtpException){
}

Answer 4

I would highly recommend you to try the FluenAssertions:
http://fluentassertions.codeplex.com/
They are simple awesome and Elegant
And they let you check the exception message (You can not do that with the ExpectedException attribute)
Example:
using FluentAssertions;
[TestMethod]
public void notifyEmailTest()
{
eMail target = new eMail("TEST Subject","TEST Body"); // TODO: Initialize to an appropriate value
target.Invoking(x => x.notifyEmail())
.ShouldThrow<YourExcpectedException>()
.WithMessage("Your expected message", FluentAssertions.Assertions.ComparisonMode.Substring);
}