Python setup.py test dependencies for custom test command

To make python setup.py test linting, testing and coverage commands, I created a custom command. However, it doesn't install the dependencies specified as tests_require anymore. How can I make both work at the same time?

class TestCommand(setuptools.Command):

    description = 'run linters, tests and create a coverage report'
    user_options = []

    def initialize_options(self):
        pass

    def finalize_options(self):
        pass

    def run(self):
        self._run(['pep8', 'package', 'test', 'setup.py'])
        self._run(['py.test', '--cov=package', 'test'])

    def _run(self, command):
        try:
            subprocess.check_call(command)
        except subprocess.CalledProcessError as error:
            print('Command failed with exit code', error.returncode)
            sys.exit(error.returncode)


def parse_requirements(filename):
    with open(filename) as file_:
        lines = map(lambda x: x.strip('\n'), file_.readlines())
    lines = filter(lambda x: x and not x.startswith('#'), lines)
    return list(lines)


if __name__ == '__main__':
    setuptools.setup(
        # ...
        tests_require=parse_requirements('requirements-test.txt'),
        cmdclass={'test': TestCommand, 'build_ext': BuildExtCommand},
    )