'Honour the longMessage attribute when generating failure messages.
If longMessage is False this means:
* Use only an explicit message if it is provided
* Otherwise use the standard message for the assert
If longMessage is True:
* Use the standard message
* If an explicit message is provided, plus \' : \' and the explicit
message'

def _formatMessage(self, msg, standardMsg):

    if msg:
        data = ('%s:\n%s' % (standardMsg, pprint.pformat(msg)))
        return data.replace('\\n', '\n')
    return standardMsg
