Change Resolver.ResolveAsync to virtual (#1523)

Author: JamesNK

src/Grpc.Net.Client/Balancer/Resolver.cs

@@ -173,7 +173,10 @@ private async Task ResolveNowAsync(CancellationToken cancellationToken)
         /// </summary>
         /// <param name="cancellationToken">A cancellation token.</param>
         /// <returns>A task.</returns>
-        protected abstract Task ResolveAsync(CancellationToken cancellationToken);
+        protected virtual Task ResolveAsync(CancellationToken cancellationToken)
+        {
+            return Task.CompletedTask;
+        }
 
         /// <summary>
         /// Releases the unmanaged resources used by the <see cref="LoadBalancer"/> and optionally releases

src/Grpc.Net.Client/Balancer/StaticResolver.cs

@@ -53,12 +53,6 @@ protected override void OnStarted()
             // Send addresses to listener once. They will never change.
             Listener(ResolverResult.ForResult(_addresses, serviceConfig: null, serviceConfigStatus: null));
         }
-
-        /// <inheritdoc />
-        protected override Task ResolveAsync(CancellationToken cancellationToken)
-        {
-            return Task.CompletedTask;
-        }
     }
 
     /// <summary>

test/Grpc.Net.Client.Tests/GrpcChannelTests.cs

@@ -836,11 +836,6 @@ public ChannelTestResolver(ResolverOptions options) : base(options.LoggerFactory
             }
 
             public ResolverOptions Options { get; }
-
-            protected override Task ResolveAsync(CancellationToken cancellationToken)
-            {
-                throw new NotImplementedException();
-            }
         }
 #endif