message: test: Remove mock error from test results.
  Fixes
diff: @@ -119,13 +119,14 @@ describe('CliRunner', (): void => {
  });
  it('writes to stderr when an error occurs.', async(): Promise<void> => {
  - jest.spyOn(process.stderr, 'write');
  + const write = jest.spyOn(process.stderr, 'write').mockImplementation((): any => null);
  loader.instantiateFromUrl.mockRejectedValueOnce(new Error('Fatal'));
  runCli();
  await new Promise((resolve): any => setImmediate(resolve));
  - expect(process.stderr.write).toHaveBeenCalledTimes(1);
  - expect(process.stderr.write).toHaveBeenCalledWith('Error: Fatal\n');
  + expect(write).toHaveBeenCalledTimes(1);
  + expect(write).toHaveBeenCalledWith('Error: Fatal\n');
  + write.mockClear();
  });
  });
  