@Test(
     expectedExceptions = IllegalArgumentException.class,
     expectedExceptionsMessageRegExp = "clientId is null or empty")
 public void testValidateRefreshTokenRequestInput_NullClientId() throws MalformedURLException {
   ctx = new AuthenticationContext(TestConfiguration.AAD_TENANT_ENDPOINT, true, service);
   ctx.acquireTokenByRefreshToken(
       "refresh_token", null, new ClientAssertion("invalid_assertion"), null);
 }
 @Test
 public void testFailedAcquireTokenRequest_ExecuteCallback() throws Throwable {
   ctx = new AuthenticationContext(TestConfiguration.AAD_UNKNOWN_TENANT_ENDPOINT, true, service);
   AuthenticationCallback ac = PowerMock.createMock(AuthenticationCallback.class);
   ac.onFailure(EasyMock.isA(Throwable.class));
   EasyMock.expectLastCall();
   PowerMock.replay(ac);
   Future<AuthenticationResult> result =
       ctx.acquireTokenByRefreshToken(
           "refresh", new ClientCredential("clientId", "clientSecret"), "resource", ac);
   try {
     result.get();
   } catch (ExecutionException ee) {
     throw ee.getCause();
   }
 }