Sets the default prompt to match the currently active unit test.

def _set_def_prompt(self):
        """Sets the default prompt to match the currently active unit test."""
        if len(self.active) > 15:
            ids = self.active.split(".")
            if len(ids) > 2:
                module, executable, compiler = ids
            else:
                module, executable = ids
                compiler = "g"
            self.prompt = "({}*.{}*.{}:{})".format(module[0:6], executable[0:6], compiler, self.group)
        else:
            self.prompt = "({}:{})".format(self.active, self.group)