compare channel creds.

Author: rmehta19

gax-java/gax-grpc/src/main/java/com/google/api/gax/grpc/InstantiatingGrpcChannelProvider.java

@@ -178,6 +178,11 @@ static void resetS2AChannelCredentials() {
     }
   }
 
+  @VisibleForTesting
+  static ChannelCredentials getS2AChannelCredentials() {
+    return s2aChannelCredentials;
+  }
+
   /*
    * Experimental feature
    *

gax-java/gax-grpc/src/test/java/com/google/api/gax/grpc/InstantiatingGrpcChannelProviderTest.java

@@ -1197,7 +1197,7 @@ void createS2ASecuredChannelCredentials_bothS2AAddressesNull_returnsNull() {
             .setS2AConfigProvider(s2aConfigProvider)
             .build();
     assertThat(provider2.createS2ASecuredChannelCredentials()).isNotNull();
-    assertEquals(provider, provider2);
+    assertEquals(provider.getS2AChannelCredentials(), provider2.getS2AChannelCredentials());
   }
 
   @Test