def startTest(self, test):
        """
        Called when a test begins to run. Records the time when it was first
        called and resets the warning cache.

        @param test: L{ITestCase}
        """
        super(Reporter, self).startTest(test)
        if self._startTime is None:
            self._startTime = self._getTime()
        self._warningCache = set()

        Called when a test begins to run. Records the time when it was first
        called and resets the warning cache.

        @param test: L{ITestCase}
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/trial/reporter.py