Using Assert::ExpectException with Native Unit Testing in VS11

The native unit testing capabilities in VS11 beta are very cool indeed.  Being mainly a managed code developer, I was left wondering how to pass a test if an expected exception is thrown (a al the [ExpectedException] attribute I’ve used with MS-TEST in managed code unit tests.  With the native unit testing capabilities in VS11, there is no ExpectedException attribute, but there is a static Assert::ExpectException method that we use to verify that our code under test throws an exception.  It accepts a lambda or a functor as a parameter.  Being a beta, I hadn’t seen too many examples, so I’ve included a couple below.

    1:          TEST_METHOD(ExpectCallThrowException)

    2:          {

    3:              auto func = [this] { throwException();};

    4:              Assert::ExpectException<int>(func);

    5:          }

    6:   

    7:          void throwException()

    8:          {

    9:              throw 1;

   10:          }

Here is a more realistic example, where my BankAccount class throws an invalid_argument exception if a zero amount is passed in as the parameter.

    1:  double BankAccount::Debit(double amount)

    2:  {

    3:      if(amount == 0)

    4:      {

    5:          throw std::invalid_argument("amount");

    6:      }

    7:      balance -= amount;

    8:      return balance;

    9:  }

   10:   

   11:  double BankAccount::Credit(double amount)

   12:  {

   13:      if(amount == 0)

   14:      {

   15:          throw std::invalid_argument("amount");

   16:      }

   17:      balance += amount;

   18:      return balance;

   19:  }

And for my test code, we have examples below of using Assert::ExpectException with a lambda, or by catching the exception ourselves and verifying in the test.

    1:      

    2:  #include <stdexcept>

    3:  #include <functional>

    4:   

    5:          TEST_METHOD(InvalidArgumentIsThrownWhenDebittingZero)

    6:          {

    7:              BankAccount* sut = new BankAccount();

    8:              double amount = 0.00;

    9:              function<double (void)> f1 = [sut] { return sut->Debit(0.00); };

   10:              Assert::ExpectException<invalid_argument>(f1);

   11:          }

   12:   

   13:          TEST_METHOD(ExceptionThrownWhenCreditAmountIsZero)

   14:          {

   15:              BankAccount* sut = new BankAccount();

   16:              double amount = 0.00;

   17:              bool exceptionThrown = false;

   18:              try

   19:              {

   20:                  sut->Credit(amount);

   21:              }catch(invalid_argument& ex)

   22:              {

   23:                  auto desc = ex.what();

   24:                  exceptionThrown = true;

   25:              }

   26:              Assert::IsTrue(exceptionThrown);

   27:          }

I haven’t seen too many examples of using Assert::ExpectException, so hopefully this is helpful.  If this all changes for the VS11 RTM, I’ll be sure to update this post.

Thanks,
-Dan