Read content of diff file.

        This is here to help with testing.

        @return: File content.
        @rtype: c{str}

def _readDiffFile(self):
        """
        Read content of diff file.

        This is here to help with testing.

        @return: File content.
        @rtype: c{str}
        """
        with open(self.diffOption) as f:
            content = f.read()
        return content