def mock_get_env_vars(env_vars_exists):
    """Mock the call to os.getenv in get_credentials"""

    expecteds = ('partner_id', 'shop_id', 'key', 'sandbox')
    credentials = dict().fromkeys(expecteds)

    if env_vars_exists:
        for expected in expecteds:
            credentials.update({expected: 'XXX'})
    return credentials