xds: Increase speed of fallback test

These changes reduce connect_then_mainServerDown_fallbackServerUp test
time from 20 seconds to 5 s by faking time for the the does-no-exist
timer.

XdsClientImpl only uses the TimeProvider for CSDS cache details, so any
implementation should be fine. FakeXdsClient provides an implementation,
so might as well use it as it is one less clock to think about.

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

@@ -335,10 +335,13 @@ private static void verifyNoSubscribers(ControlPlaneRule rule) {
 
   // This test takes a long time because of the 16 sec timeout for non-existent resource
   @Test
-  public void connect_then_mainServerDown_fallbackServerUp() throws InterruptedException {
+  public void connect_then_mainServerDown_fallbackServerUp() throws Exception {
     mainXdsServer.restartXdsServer();
     fallbackServer.restartXdsServer();
-    xdsClient = xdsClientPool.getObject();
+    XdsClientImpl xdsClient = CommonBootstrapperTestUtils.createXdsClient(
+        new GrpcBootstrapperImpl().bootstrap(defaultBootstrapOverride()),
+        DEFAULT_XDS_TRANSPORT_FACTORY, fakeClock, new ExponentialBackoffPolicy.Provider(),
+        MessagePrinter.INSTANCE, xdsClientMetricReporter);
 
     xdsClient.watchXdsResource(XdsListenerResource.getInstance(), MAIN_SERVER, ldsWatcher);
 
@@ -349,7 +352,12 @@ public void connect_then_mainServerDown_fallbackServerUp() throws InterruptedExc
     verify(rdsWatcher, timeout(5000)).onChanged(any());
 
     mainXdsServer.getServer().shutdownNow();
-    TimeUnit.SECONDS.sleep(5); // TODO(lsafran) Use FakeClock so test runs faster
+    // Sleep for the ADS stream disconnect to be processed and for the retry to fail. Between those
+    // two sleeps we need the fakeClock to progress by 1 second to restart the ADS stream.
+    for (int i = 0; i < 5; i++) {
+      fakeClock.forwardTime(1000, TimeUnit.MILLISECONDS);
+      TimeUnit.SECONDS.sleep(1);
+    }
 
     // Shouldn't do fallback since all watchers are loaded
     verify(ldsWatcher, never()).onChanged(
@@ -372,7 +380,7 @@ public void connect_then_mainServerDown_fallbackServerUp() throws InterruptedExc
         XdsListenerResource.LdsUpdate.forApiListener(FALLBACK_HTTP_CONNECTION_MANAGER));
     verify(ldsWatcher2, timeout(5000)).onChanged(
         XdsListenerResource.LdsUpdate.forApiListener(FALLBACK_HTTP_CONNECTION_MANAGER));
-    verify(cdsWatcher, timeout(16000)).onChanged(any());
+    verify(cdsWatcher, timeout(5000)).onChanged(any());
 
     xdsClient.watchXdsResource(
         XdsRouteConfigureResource.getInstance(), FALLBACK_RDS_NAME, rdsWatcher3);
@@ -381,7 +389,10 @@ public void connect_then_mainServerDown_fallbackServerUp() throws InterruptedExc
     // Test that resource defined in main but not fallback is handled correctly
     xdsClient.watchXdsResource(
         XdsClusterResource.getInstance(), CLUSTER_NAME, cdsWatcher2);
-    verify(cdsWatcher2, timeout(16000)).onResourceDoesNotExist(eq(CLUSTER_NAME));
+    verify(cdsWatcher2, never()).onResourceDoesNotExist(eq(CLUSTER_NAME));
+    fakeClock.forwardTime(15000, TimeUnit.MILLISECONDS); // Does not exist timer
+    verify(cdsWatcher2, timeout(5000)).onResourceDoesNotExist(eq(CLUSTER_NAME));
+    xdsClient.shutdown();
   }
 
   @Test

xds/src/test/java/io/grpc/xds/client/CommonBootstrapperTestUtils.java

@@ -23,7 +23,6 @@
 import io.grpc.internal.BackoffPolicy;
 import io.grpc.internal.FakeClock;
 import io.grpc.internal.JsonParser;
-import io.grpc.internal.TimeProvider;
 import io.grpc.xds.client.Bootstrapper.ServerInfo;
 import io.grpc.xds.internal.security.CommonTlsContextTestsUtil;
 import io.grpc.xds.internal.security.TlsContextManagerImpl;
@@ -32,28 +31,12 @@
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
-import java.util.concurrent.TimeUnit;
 import javax.annotation.Nullable;
 
 public class CommonBootstrapperTestUtils {
   private static final ChannelCredentials CHANNEL_CREDENTIALS = InsecureChannelCredentials.create();
   private static final String SERVER_URI_CUSTOM_AUTHORITY = "trafficdirector2.googleapis.com";
   private static final String SERVER_URI_EMPTY_AUTHORITY = "trafficdirector3.googleapis.com";
-
-  private static final long TIME_INCREMENT = TimeUnit.SECONDS.toNanos(1);
-
-  /** Fake time provider increments time TIME_INCREMENT each call. */
-  private static TimeProvider newTimeProvider() {
-    return new TimeProvider() {
-      private long count;
-
-      @Override
-      public long currentTimeNanos() {
-        return ++count * TIME_INCREMENT;
-      }
-    };
-  }
-
   private static final String FILE_WATCHER_CONFIG = "{\"path\": \"/etc/secret/certs\"}";
   private static final String MESHCA_CONFIG =
       "{\n"
@@ -183,14 +166,28 @@ public static XdsClientImpl createXdsClient(List<String> serverUris,
                                               BackoffPolicy.Provider backoffPolicyProvider,
                                               MessagePrettyPrinter messagePrinter,
                                               XdsClientMetricReporter xdsClientMetricReporter) {
-    Bootstrapper.BootstrapInfo bootstrapInfo = buildBootStrap(serverUris);
+    return createXdsClient(
+        buildBootStrap(serverUris),
+        xdsTransportFactory,
+        fakeClock,
+        backoffPolicyProvider,
+        messagePrinter,
+        xdsClientMetricReporter);
+  }
+
+  public static XdsClientImpl createXdsClient(Bootstrapper.BootstrapInfo bootstrapInfo,
+                                              XdsTransportFactory xdsTransportFactory,
+                                              FakeClock fakeClock,
+                                              BackoffPolicy.Provider backoffPolicyProvider,
+                                              MessagePrettyPrinter messagePrinter,
+                                              XdsClientMetricReporter xdsClientMetricReporter) {
     return new XdsClientImpl(
         xdsTransportFactory,
         bootstrapInfo,
         fakeClock.getScheduledExecutorService(),
         backoffPolicyProvider,
         fakeClock.getStopwatchSupplier(),
-        newTimeProvider(),
+        fakeClock.getTimeProvider(),
         messagePrinter,
         new TlsContextManagerImpl(bootstrapInfo),
         xdsClientMetricReporter);