Refactor event capturing in submit tests for more precise assertions

Factor the event capturing out to a new class, EventRecorder, which
listens to the events and records those that are of type RefEvent.

Events are recorded in a map keyed on a combination of the event type,
project name and ref (branch name). In each map entry the received
events are stored in a list.

This allows us to make assertions about the events that were received
for a project and branch, and in which order they were received.

Convert the existing tests of change-merged events to use the new
class.

Also extend the submit-by-fast-forward tests to assert that when a
stack of changes is submitted by fast-forward, there was only one
ref-updated event for that project/branch and it contains:

  - old ref: the sha1 of the branch's original HEAD
  - new ref: the sha1 of the change at the top of the stack

Bug: Issue 4123
Change-Id: Ic978fb28fda601c9ab5897e0a0e2f9280d59216c

gerrit-acceptance-framework/src/test/java/com/google/gerrit/acceptance/EventRecorder.java

@@ -0,0 +1,119 @@
+// Copyright (C) 2016 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.gerrit.acceptance;
+
+import static com.google.common.truth.Truth.assertThat;
+import static org.eclipse.jgit.lib.Constants.R_HEADS;
+
+import com.google.common.base.Predicate;
+import com.google.common.collect.FluentIterable;
+import com.google.common.collect.LinkedListMultimap;
+import com.google.common.collect.Multimap;
+import com.google.gerrit.common.UserScopedEventListener;
+import com.google.gerrit.extensions.registration.DynamicSet;
+import com.google.gerrit.extensions.registration.RegistrationHandle;
+import com.google.gerrit.server.CurrentUser;
+import com.google.gerrit.server.IdentifiedUser;
+import com.google.gerrit.server.events.ChangeMergedEvent;
+import com.google.gerrit.server.events.Event;
+import com.google.gerrit.server.events.RefEvent;
+import com.google.gerrit.server.events.RefUpdatedEvent;
+import com.google.inject.Inject;
+import com.google.inject.Singleton;
+
+import java.util.Collection;
+import java.util.List;
+
+public class EventRecorder {
+  private final RegistrationHandle eventListenerRegistration;
+  private final Multimap<String, RefEvent> recordedEvents;
+
+  @Singleton
+  public static class Factory {
+    private final DynamicSet<UserScopedEventListener> eventListeners;
+    private final IdentifiedUser.GenericFactory userFactory;
+
+    @Inject
+    Factory(DynamicSet<UserScopedEventListener> eventListeners,
+        IdentifiedUser.GenericFactory userFactory) {
+      this.eventListeners = eventListeners;
+      this.userFactory = userFactory;
+    }
+
+    public EventRecorder create(TestAccount user) {
+      return new EventRecorder(eventListeners, userFactory.create(user.id));
+    }
+  }
+
+  public EventRecorder(DynamicSet<UserScopedEventListener> eventListeners,
+      final IdentifiedUser user) {
+    recordedEvents = LinkedListMultimap.create();
+
+    eventListenerRegistration = eventListeners.add(
+        new UserScopedEventListener() {
+          @Override
+          public void onEvent(Event e) {
+            if (e instanceof RefEvent) {
+              RefEvent event = (RefEvent) e;
+              String key = key(event.getType(), event.getProjectNameKey().get(),
+                  event.getRefName());
+              recordedEvents.put(key, event);
+            }
+          }
+
+          @Override
+          public CurrentUser getUser() {
+            return user;
+          }
+        });
+  }
+
+  private static String key(String type, String project, String ref) {
+    return String.format("%s-%s-%s", type, project, ref);
+  }
+
+  public RefUpdatedEvent getOneRefUpdate(String project, String refName) {
+    String key = key(RefUpdatedEvent.TYPE, project, refName);
+    assertThat(recordedEvents).containsKey(key);
+    Collection<RefEvent> events = recordedEvents.get(key);
+    assertThat(events).hasSize(1);
+    Event e = events.iterator().next();
+    assertThat(e).isInstanceOf(RefUpdatedEvent.class);
+    return (RefUpdatedEvent) e;
+  }
+
+  public ChangeMergedEvent getOneChangeMerged(String project, String branch,
+      final String changeNumber) throws Exception {
+    String key = key(ChangeMergedEvent.TYPE, project,
+        branch.startsWith(R_HEADS) ? branch : R_HEADS + branch);
+    assertThat(recordedEvents).containsKey(key);
+    List<RefEvent> events = FluentIterable
+        .from(recordedEvents.get(key))
+        .filter(new Predicate<RefEvent>() {
+          @Override
+          public boolean apply(RefEvent input) {
+            assertThat(input).isInstanceOf(ChangeMergedEvent.class);
+            ChangeMergedEvent e = (ChangeMergedEvent) input;
+            return e.change.get().number.equals(changeNumber);
+          }})
+        .toList();
+    assertThat(events).hasSize(1);
+    return (ChangeMergedEvent) events.get(0);
+  }
+
+  public void close() {
+    eventListenerRegistration.remove();
+  }
+}