core/test: re-enable tests for panic mode. (#5879)

panic mode was temporarily disabled by #4152 and re-enabled by #4245,
but the tests were not.  This has caused a few test code that was
broken but not executed at all.

core/src/main/java/io/grpc/internal/ManagedChannelImpl.java

@@ -791,6 +791,11 @@ final class ManagedChannelImpl extends ManagedChannel implements
     channelStateManager.gotoState(TRANSIENT_FAILURE);
   }
 
+  @VisibleForTesting
+  boolean isInPanicMode() {
+    return panicMode;
+  }
+
   // Called from syncContext
   private void updateSubchannelPicker(SubchannelPicker newPicker) {
     subchannelPicker = newPicker;

core/src/test/java/io/grpc/internal/ManagedChannelImplTest.java

@@ -136,7 +136,6 @@ import java.util.logging.Logger;
 import javax.annotation.Nullable;
 import org.junit.After;
 import org.junit.Assert;
-import org.junit.Assume;
 import org.junit.Before;
 import org.junit.Rule;
 import org.junit.Test;
@@ -269,6 +268,7 @@ public class ManagedChannelImplTest {
   private ChannelBuilder channelBuilder;
   private boolean requestConnection = true;
   private BlockingQueue<MockClientTransportInfo> transports;
+  private boolean panicExpected;
 
   private ArgumentCaptor<ClientStreamListener> streamListenerCaptor =
       ArgumentCaptor.forClass(ClientStreamListener.class);
@@ -338,6 +338,9 @@ public class ManagedChannelImplTest {
     assertTrue(timer.getDueTasks() + " should be empty", timer.getDueTasks().isEmpty());
     assertEquals(executor.getPendingTasks() + " should be empty", 0, executor.numPendingTasks());
     if (channel != null) {
+      if (!panicExpected) {
+        assertFalse(channel.isInPanicMode());
+      }
       channel.shutdownNow();
       channel = null;
     }
@@ -405,15 +408,8 @@ public class ManagedChannelImplTest {
   @SuppressWarnings("deprecation")
   public void createSubchannel_old_propagateSubchannelStatesToOldApi() {
     createChannel();
-    final AtomicReference<Subchannel> subchannelCapture = new AtomicReference<>();
-    helper.getSynchronizationContext().execute(new Runnable() {
-        @Override
-        public void run() {
-          subchannelCapture.set(helper.createSubchannel(addressGroup, Attributes.EMPTY));
-        }
-      });
 
-    Subchannel subchannel = subchannelCapture.get();
+    Subchannel subchannel = helper.createSubchannel(addressGroup, Attributes.EMPTY);
     subchannel.requestConnection();
 
     verify(mockTransportFactory)
@@ -427,6 +423,15 @@ public class ManagedChannelImplTest {
 
     verify(mockLoadBalancer).handleSubchannelState(
         same(subchannel), eq(ConnectivityStateInfo.forNonError(READY)));
+
+    channel.shutdown();
+    verify(mockLoadBalancer).shutdown();
+    subchannel.shutdown();
+
+    verify(mockLoadBalancer, atLeast(0)).canHandleEmptyAddressListFromNameResolution();
+    verify(mockLoadBalancer, atLeast(0)).handleNameResolutionError(any(Status.class));
+    // handleSubchannelState() should not be called after shutdown()
+    verifyNoMoreInteractions(mockLoadBalancer);
   }
 
   @Test
@@ -773,9 +778,17 @@ public class ManagedChannelImplTest {
 
     channel.shutdown();
     verify(mockLoadBalancer).shutdown();
+    verifyNoMoreInteractions(stateListener1, stateListener2);
 
-    // No more callback should be delivered to LoadBalancer after it's shut down
+    // LoadBalancer will normally shutdown all subchannels
+    subchannel1.shutdown();
+    subchannel2.shutdown();
+
+    // No more callback are delivered to LoadBalancer or the state listeners after it's shut down
+    transportInfo1.listener.transportShutdown(Status.UNAVAILABLE);
     transportInfo2.listener.transportReady();
+    verifyNoMoreInteractions(stateListener1, stateListener2);
+
     resolver.listener.onError(resolutionError);
     resolver.resolved();
     verifyNoMoreInteractions(mockLoadBalancer);
@@ -2213,8 +2226,8 @@ public class ManagedChannelImplTest {
     assertEquals(TRANSIENT_FAILURE, channel.getState(true));
     verifyPanicMode(panicReason);
 
-    // No new resolver or balancer are created
-    verifyNoMoreInteractions(mockLoadBalancerProvider);
+    // Besides the resolver created initially, no new resolver or balancer are created.
+    verify(mockLoadBalancerProvider).newLoadBalancer(any(Helper.class));
     assertThat(nameResolverFactory.resolvers).isEmpty();
 
     // A misbehaving balancer that calls updateBalancingState() after it's shut down will not be
@@ -2223,7 +2236,12 @@ public class ManagedChannelImplTest {
     verifyPanicMode(panicReason);
 
     // Cannot be revived by exitIdleMode()
-    channel.exitIdleMode();
+    channel.syncContext.execute(new Runnable() {
+        @Override
+        public void run() {
+          channel.exitIdleMode();
+        }
+      });
     verifyPanicMode(panicReason);
 
     // Can still shutdown normally
@@ -2270,11 +2288,11 @@ public class ManagedChannelImplTest {
     executor.runDueTasks();
     verifyCallListenerClosed(mockCallListener, Status.Code.INTERNAL, panicReason);
     verifyCallListenerClosed(mockCallListener2, Status.Code.INTERNAL, panicReason);
+    panicExpected = true;
   }
 
   private void verifyPanicMode(Throwable cause) {
-    Assume.assumeTrue("Panic mode disabled to resolve issues with some tests. See #3293", false);
-
+    panicExpected = true;
     @SuppressWarnings("unchecked")
     ClientCall.Listener<Integer> mockListener =
         (ClientCall.Listener<Integer>) mock(ClientCall.Listener.class);