单元测试如何确认已抛出异常

Question

Im writing a unit test for a c# class, One of my tests should cause the method to throw an exception when the data is added. How can i use my unit test to confirm that the exception has been thrown?

Answer 1

It depends on what unit test framework you're using. In all cases you could do something like:

[Test]
public void MakeItGoBang()
{
     Foo foo = new Foo();
     try
     {
         foo.Bang();
         Assert.Fail("Expected exception");
     }
     catch (BangException)
     { 
         // Expected
     }
}

In some frameworks there's an attribute you can add to the test method to express the expected exception, or there may be a method, such as:

[Test]
public void MakeItGoBang()
{
     Foo foo = new Foo();
     Assert.Throws<BangException>(() => foo.Bang());
}

It's nicer to limit the scope like this, as if you apply it to the whole test, the test could pass even if the wrong line threw the exception.

Answer 2

[ExpectedException(typeof(System.Exception))]

for Visual Studio Unit Testing Framework.

See MSDN :

The test method will pass if the expected exception is thrown.

The test will fail if the thrown exception inherits from the expected exception.

Answer 3

If you want to follow the triple-A pattern (arrange, act, assert), you could go for this, regardless of test framework:

[Test]
public void MyMethod_DodgyStuffDone_ThrowsRulesException() {

    // arrange
    var myObject = CreateObject();
    Exception caughtException = null;

    // act
    try {
        myObject.DoDodgyStuff();
    }
    catch (Exception ex) {
        caughtException = ex;
    }

    // assert
    Assert.That(caughtException, Is.Not.Null);
    Assert.That(caughtException, Is.TypeOf<RulesException>());
    Assert.That(caughtException.Message, Is.EqualTo("My Error Message"));
}

Answer 4

If you are using Nunit, you can tag your test with

[ExpectedException( "System.ArgumentException" ) )]

Answer 5

You can usee Verify() method for Unit Testing and compare your Exception Message from return type.

InterfaceMockObject.Verify(i =>i.Method(It.IsAny<>())), "Your received Exception Message");

You need to write some classname or datatype in It.IsAny<> block