Run the system test suite.

def system(session):
    """Run the system test suite."""

    # Sanity check: Only run system tests if the environment variable is set.
    if not os.environ.get('GOOGLE_APPLICATION_CREDENTIALS', ''):
        session.skip('Credentials must be set via environment variable.')

    # Install all test dependencies, then install this package into the
    # virtualenv's dist-packages.
    session.install('pytest')
    session.install('-e', os.path.join('..', 'test_utils'))
    for local_dep in LOCAL_DEPS:
        session.install('-e', local_dep)
    session.install('-e', '.[pandas,fastavro]')

    # Run py.test against the system tests.
    session.run('py.test', '--quiet', 'tests/system/')