Polish comments for setKeepaliveWithInterval

src/objective-c/GRPCClient/GRPCCall+ChannelArg.h

@@ -46,9 +46,11 @@ typedef NS_ENUM(NSInteger, GRPCCompressAlgorithm) {
 + (void)setDefaultCompressMethod:(GRPCCompressAlgorithm)algorithm
                          forhost:(nonnull NSString *)host;
 
-/** Configure keepalive timeout parameters. A client ping after \a interval ms to check if the
- * transport is still alive. After waiting for \a timeout ms, if the client does not receive the
- * ping ack, it closes the transport. */
+/** Enable keepalive and configure keepalive parameters. A user should call this function once to
+ * enable keepalive for a particular host. gRPC client sends a ping after every \a interval ms to
+ * check if the transport is still alive. After waiting for \a timeout ms, if the client does not
+ * receive the ping ack, it closes the transport; all pending calls to this host will fail with
+ * error GRPC_STATUS_INTERNAL with error information "keepalive watchdog timeout". */
 + (void)setKeepaliveWithInterval:(int)interval
                          timeout:(int)timeout
                          forHost:(nonnull NSString *)host;

src/objective-c/tests/InteropTests.m

@@ -515,6 +515,9 @@ BOOL isRemoteInteropTest(NSString *host) {
     } else {
       // Keepalive should kick after 1s elapsed and fails the call.
       XCTAssertNotNil(error);
+      XCTAssertEqual(error.code, GRPC_STATUS_INTERNAL);
+      XCTAssertEqualObjects(error.localizedDescription, @"keepalive watchdog timeout",
+                            @"Unexpected failure that is not keepalive watchdog timeout.");
       XCTAssertTrue(done);
       [expectation fulfill];
     }