Add test for multiple xds clients used by CsdsService

xds/src/test/java/io/grpc/xds/CsdsServiceTest.java

@@ -54,8 +54,8 @@
 import io.grpc.xds.client.XdsClient.ResourceMetadata;
 import io.grpc.xds.client.XdsClient.ResourceMetadata.ResourceMetadataStatus;
 import io.grpc.xds.client.XdsResourceType;
+import java.util.ArrayList;
 import java.util.Collection;
-import java.util.Collections;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
@@ -269,6 +269,31 @@ public void streamClientStatus_onClientError() {
       assertThat(responseObserver.getError()).isNull();
     }
 
+    @Test
+    public void multipleXdsClients() {
+      FakeXdsClient xdsClient1 = new FakeXdsClient();
+      FakeXdsClient xdsClient2 = new FakeXdsClient();
+      Map<String, XdsClient> clientMap = new HashMap<>();
+      clientMap.put("target1", xdsClient1);
+      clientMap.put("target2", xdsClient2);
+      FakeXdsClientPoolFactory factory = new FakeXdsClientPoolFactory(clientMap);
+      CsdsService csdsService = new CsdsService(factory);
+      grpcServerRule.getServiceRegistry().addService(csdsService);
+
+      StreamRecorder<ClientStatusResponse> responseObserver = StreamRecorder.create();
+      StreamObserver<ClientStatusRequest> requestObserver =
+          csdsAsyncStub.streamClientStatus(responseObserver);
+
+      requestObserver.onNext(REQUEST);
+      requestObserver.onCompleted();
+
+      List<ClientStatusResponse> responses = responseObserver.getValues();
+      assertThat(responses).hasSize(1);
+      Collection<String> targets = verifyMultiResponse(responses.get(0), 2);
+      assertThat(targets).containsExactly("target1", "target2");
+      responseObserver.onCompleted();
+    }
+
     private void verifyResponse(ClientStatusResponse response) {
       assertThat(response.getConfigCount()).isEqualTo(1);
       ClientConfig clientConfig = response.getConfig(0);
@@ -277,6 +302,20 @@ private void verifyResponse(ClientStatusResponse response) {
       assertThat(clientConfig.getClientScope()).isEmpty();
     }
 
+    private Collection<String> verifyMultiResponse(ClientStatusResponse response, int numExpected) {
+      assertThat(response.getConfigCount()).isEqualTo(numExpected);
+
+      List<String> clientScopes = new ArrayList<>();
+      for (int i = 0; i < numExpected; i++) {
+        ClientConfig clientConfig = response.getConfig(i);
+        verifyClientConfigNode(clientConfig);
+        verifyClientConfigNoResources(XDS_CLIENT_NO_RESOURCES, clientConfig);
+        clientScopes.add(clientConfig.getClientScope());
+      }
+
+      return clientScopes;
+    }
+
     private void verifyRequestInvalidResponseStatus(Status status) {
       assertThat(status.getCode()).isEqualTo(Code.INVALID_ARGUMENT);
       assertThat(status.getDescription()).isEqualTo("node_matchers not supported");
@@ -471,20 +510,31 @@ public Map<String, XdsResourceType<?>> getSubscribedResourceTypesWithTypeUrl() {
   }
 
   private static class FakeXdsClientPoolFactory implements XdsClientPoolFactory {
-    @Nullable private final XdsClient xdsClient;
-    private static final List<String> TARGETS = Collections.singletonList("");
+    private final Map<String, XdsClient> xdsClientMap = new HashMap<>();
+    private boolean isOldStyle
+        ;
 
     private FakeXdsClientPoolFactory(@Nullable XdsClient xdsClient) {
-      this.xdsClient = xdsClient;
+      if (xdsClient != null) {
+        xdsClientMap.put("", xdsClient);
+      }
+      isOldStyle = true;
+    }
+
+    private FakeXdsClientPoolFactory(Map<String,XdsClient> xdsClientMap) {
+      this.xdsClientMap.putAll(xdsClientMap);
+      isOldStyle = false;
     }
 
     @Override
     @Nullable
-    public ObjectPool<XdsClient> get(String notUsedTarget) {
+    public ObjectPool<XdsClient> get(String target) {
+      String targetToUse = isOldStyle ? "" : target;
+
       return new ObjectPool<XdsClient>() {
         @Override
         public XdsClient getObject() {
-          return xdsClient;
+          return xdsClientMap.get(targetToUse);
         }
 
         @Override
@@ -496,7 +546,7 @@ public XdsClient returnObject(Object object) {
 
     @Override
     public List<String> getTargets() {
-      return TARGETS;
+      return new ArrayList<>(xdsClientMap.keySet());
     }
 
     @Override