Python, mock: raise exception

Question

I’m having issues raising an exception from a function in my test:

### Implemetation
def MethodToTest():
    myVar = StdObject()
    try:
        myVar.raiseError() # <--- here
        return True
    except Exception as e:
        # ... code to test
        return False

### Test file
@patch('stdLib.StdObject', autospec=True)
def test_MethodeToTest(self, mockedObjectConstructor):
    mockedObj = mockedObjectConstructor.return_value
    mockedObj.raiseError.side_effect = Exception('Test') # <--- do not work
    ret = MethodToTest()
    assert ret is False

I would like to raiseError() function to raise an error.

I found several examples on SO, but none that matched my need.

Asked By: user4780495

||

Source

Answer 1

I changed

@patch('stdLib.StdObject', autospec=True)

to

@patch('stdLib.StdObject', **{'return_value.raiseError.side_effect': Exception()})

and removed the # <--- do not work line.

It’s now working.

This is a good example.

EDIT:

mockedObj.raiseError.side_effect = Mock(side_effect=Exception('Test'))

also works.

Answered By: user4780495

Answer 2

Ok, your answer you provided is valid, but you changed how you did it (which is fine. To fix your original problem, you need to assign a function to side_effect, not the results or an object:

def my_side_effect():
    raise Exception("Test")

@patch('stdLib.StdObject', autospec=True)
def test_MethodeToTest(self, mockedObjectConstructor):
    mockedObj = mockedObjectConstructor.return_value
    mockedObj.raiseError.side_effect = my_side_effect # <- note no brackets, 
    ret = MethodToTest()
    assert ret is False

Hope that helps. Note, if the target method takes args, the side effect needs to take args as well (I believe).

Answered By: Jmons

Python, mock: raise exception

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