Mock testing try/except with print statements

Question

I am currently writing a unit test for my Python2 script. I am having trouble writing a test case that catches both the sys.exit and the print statement to validate the exception. Any help would be appreciated.

except ParseError, e:
        if len(self.args.password) == 0:
            print('Some Message')

        print 'Login response error'
        sys.exit(1)

Answer 1

You can mock sys calls and make assertions over them.

For example you can patch the sys.exit method in your test and then assert that it was called as follows:

@patch('sys.exit')
def test_whatever(exit_mock):
    // force the exception
    assert exit_mock.call_count == 1

For the print statement you can mock the sys.stdout call. A very concise example can be found in the Python cookbook book so I will not copy paste it here.