Add test for returned debug information

src/objective-c/tests/GRPCClientTests.m

@@ -591,4 +591,39 @@ static GRPCProtoMethod *kFullDuplexCallMethod;
   [self testTimeoutBackoffWithTimeout:0.3 Backoff:0.7];
 }
 
+- (void)testErrorDebugInformation {
+  __weak XCTestExpectation *expectation = [self expectationWithDescription:@"RPC unauthorized."];
+
+  RMTSimpleRequest *request = [RMTSimpleRequest message];
+  request.fillUsername = YES;
+  request.fillOauthScope = YES;
+  GRXWriter *requestsWriter = [GRXWriter writerWithValue:[request data]];
+
+  GRPCCall *call = [[GRPCCall alloc] initWithHost:kRemoteSSLHost
+                                             path:kUnaryCallMethod.HTTPPath
+                                   requestsWriter:requestsWriter];
+
+  call.oauth2AccessToken = @"bogusToken";
+
+  id<GRXWriteable> responsesWriteable =
+  [[GRXWriteable alloc] initWithValueHandler:^(NSData *value) {
+    XCTFail(@"Received unexpected response: %@", value);
+  }
+                           completionHandler:^(NSError *errorOrNil) {
+                             XCTAssertNotNil(errorOrNil, @"Finished without error!");
+                             NSDictionary *userInfo = errorOrNil.userInfo;
+                             NSString *debugInformation = userInfo[NSDebugDescriptionErrorKey];
+                             XCTAssertNotNil(debugInformation);
+                             XCTAssertNotEqual([debugInformation length], 0);
+                             NSString *challengeHeader = call.oauth2ChallengeHeader;
+                             XCTAssertGreaterThan(challengeHeader.length, 0, @"No challenge in response headers %@",
+                                                  call.responseHeaders);
+                             [expectation fulfill];
+                           }];
+
+  [call startWithWriteable:responsesWriteable];
+
+  [self waitForExpectationsWithTimeout:TEST_TIMEOUT handler:nil];
+}
+
 @end