Unit Testing : [ExpectedException]

Hi All,

In this post I’ll explain what you need to do if you have to ensure that a particular exception must be thrown by your C# code.

The reason why I am writing this post is that some people mistakenly use keyword ExpectedException as given below:

[TestMethod]

[ExpectedException(typeof(ApplicationException), "Game has already Concluded, Start new Game !")]

public void FirstTwoRows()

{

  GameEngine ttt = new GameEngine();

  Assert.IsTrue(ttt.RecordMove('a', 3), "This is not a winning move");

  //Following line should throw Application Exception

  Assert.IsFalse(ttt.RecordMove('b', 6), "This is not a winning move");

}

Q: What is wrong with this code?

A: This test method will not fail if you get the specified Exception, but it will also pass when you don’t get it at all.

Q: So, whats the fix?

A:  You also need to add Assert.Fail after the line where you are expecting the exception.

[TestMethod]

[ExpectedException(typeof(ApplicationException), "Game has already Concluded, Start new Game !")]

public void FirstTwoRows()

{

  GameEngine ttt = new GameEngine();

  Assert.IsTrue(ttt.RecordMove('a', 3), "This is not a winning move");

  //Following line should throw Application Exception

  Assert.IsFalse(ttt.RecordMove('b', 6), "This is not a winning move");

  Assert.Fail("Above line should have thrown Exception of given type");

}

 I hope this small change will save lot of time for you and make your Test driven Development even better.

Namaste (Greetings)

Anugrah Atreya

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