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I'm looking for a way to catch exceptions globally in my NUnit project class library. So if one of my unit tests throws an exception, I can catch it in one spot. I don't want to surround each of my tests with a try/catch block. The reason I'm doing this is to print a nice error message with an explanation of the stack trace. In ASP.NET they have a method called Application_Error in Global.asax that does this sort of thing.

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2 Answers 2

up vote 4 down vote accepted
  1. You can create an Even listener: EventListeners (NUnit 2.4.4)

Interface

The extension object passed to Install must implement the EventListener interface:

public interface EventListener
{
    void RunStarted( string name, int testCount );
    void RunFinished( TestResult result );
    void RunFinished( Exception exception );
    void TestStarted(TestName testName);
    void TestFinished(TestResult result);
    void SuiteStarted(TestName testName);
    void SuiteFinished(TestResult result);
    void UnhandledException( Exception exception );
    void TestOutput(TestOutput testOutput);
}
  1. You can make the try/catch block less ugly using the delegates (lambda expression) and closures.

Here is how it works:

    public void Try(Action testCode)
    {
        try
        {
            testCode();
        }
        catch (Exception e)
        {
            Console.WriteLine("Nice Error Here: " + e.Message);
        }
    }

    [Test]
    public void TestO1()
    {
        int actual = 5;
        int expected = 4;
        Assert.AreEqual(expected, actual);
    }

    [Test]
    public void TestO2()
    {
        int actual = 5;
        int expected = 4;
        Try( () => Assert.AreEqual(expected, actual) );
    }

The method Try accepts the code as a parameter and executes it in the try block. So, in the catch block you can apply any necessary formatting.

The method TestO1 is just a usual unit test without any tricks.

The TestO2 has the assertion wrapped with the method Try:

Try( () => any line of code here );

It will be the same try/catch, but now I don’t need to write a lot of ugly code.

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The EventListener is the way to go. However there is a knack: the UnhandledException will not be fired when an Assertion in your test fails. Rather use the TestFinished event to handle failed tests:

public void TestFinished(TestResult result)
{
    if (result.Executed && result.IsFailure)
    {
        Console.WriteLine(string.Format("Failure in test {0}", result.Name));
        Console.WriteLine(result.Message);
    }
}
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