Show source code around the current trace frame location.

        Parameters:
            context: int    number of lines to show above and below trace location
                            (default: 5)

def list_source_code(self, context: int = 5) -> None:
        """Show source code around the current trace frame location.

        Parameters:
            context: int    number of lines to show above and below trace location
                            (default: 5)
        """
        self._verify_entrypoint_selected()

        current_trace_frame = self.trace_tuples[
            self.current_trace_frame_index
        ].trace_frame

        filename = os.path.join(self.repository_directory, current_trace_frame.filename)
        file_lines: List[str] = []

        try:
            # Use readlines instead of enumerate(file) because mock_open
            # doesn't support __iter__ until python 3.7.1.
            with open(filename, "r") as file:
                file_lines = file.readlines()
        except FileNotFoundError:
            self.warning(f"Couldn't open {filename}.")
            return

        self._output_file_lines(current_trace_frame, file_lines, context)