A interface will be called when visiting a module.

        @param node: node of current module

def visit_module(self, node):
        """
        A interface will be called when visiting a module.

        @param node: node of current module
        """
        if not node.file_stream:
            # failed to open the module
            return
        text = node.file_stream.read()
        self._checkCopyright(text, node)
        if not isTestModule(node.name) and moduleNeedsTests:
            self._checkTestReference(text, node)