@Test
public void testPostAccessTokenRequestSingleRole() {

    System.setProperty(FilePrivateKeyStore.ATHENZ_PROP_PRIVATE_KEY, "src/test/resources/unit_test_zts_at_private.pem");
    CloudStore cloudStore = new CloudStore();
    cloudStore.setHttpClient(null);
    ZTSImpl ztsImpl = new ZTSImpl(cloudStore, store);
    // set back to our zts rsa private key
    System.setProperty(FilePrivateKeyStore.ATHENZ_PROP_PRIVATE_KEY, "src/test/resources/unit_test_zts_private.pem");
    SignedDomain signedDomain = createSignedDomain("coretech", "weather", "storage", true);
    store.processDomain(signedDomain, false);
    Principal principal = SimplePrincipal.create("user_domain", "user",
            "v=U1;d=user_domain;n=user;s=signature", 0, null);
    ResourceContext context = createResourceContext(principal);
    AccessTokenResponse resp = ztsImpl.postAccessTokenRequest(context,
            "grant_type=client_credentials&scope=coretech:role.writers");
    assertNotNull(resp);
    assertNull(resp.getScope());
}