TaskStorage: Fix assertContainsExactly

Update private helper assertContainsExactly() to ensure that we
have exactly one element in the list and also make it generic so
that it can be used against any list, for example listWaiting()
or listRunning()

Change-Id: I93b9f220dd865decbf8fd18240e5a47fb2042115

src/test/java/com/googlesource/gerrit/plugins/replication/ReplicationTasksStorageTest.java

diff --git a/src/test/java/com/googlesource/gerrit/plugins/replication/ReplicationTasksStorageTest.java b/src/test/java/com/googlesource/gerrit/plugins/replication/ReplicationTasksStorageTest.java
index 70dd65c..d69ace0 100644
--- a/src/test/java/com/googlesource/gerrit/plugins/replication/ReplicationTasksStorageTest.java
+++ b/src/test/java/com/googlesource/gerrit/plugins/replication/ReplicationTasksStorageTest.java
@@ -25,6 +25,7 @@
 import java.net.URISyntaxException;
 import java.nio.file.FileSystem;
 import java.nio.file.Path;
+import java.util.List;
 import java.util.Objects;
 import org.eclipse.jgit.transport.URIish;
 import org.junit.After;
@@ -65,7 +66,7 @@
   @Test
   public void canListWaitingUpdate() throws Exception {
     storage.create(REF_UPDATE);
-    assertContainsExactly(storage, REF_UPDATE);
+    assertContainsExactly(storage.list(), REF_UPDATE);
   }
 
   @Test
@@ -84,8 +85,8 @@
     assertThat(persistedView.list()).isEmpty();
 
     storage.create(REF_UPDATE);
-    assertContainsExactly(storage, REF_UPDATE);
-    assertContainsExactly(persistedView, REF_UPDATE);
+    assertContainsExactly(storage.list(), REF_UPDATE);
+    assertContainsExactly(persistedView.list(), REF_UPDATE);
 
     storage.start(uriUpdates);
     storage.finish(uriUpdates);
@@ -98,7 +99,7 @@
     String key = storage.create(REF_UPDATE);
     String secondKey = storage.create(REF_UPDATE);
     assertEquals(key, secondKey);
-    assertContainsExactly(storage, REF_UPDATE);
+    assertContainsExactly(storage.list(), REF_UPDATE);
   }
 
   @Test
@@ -131,7 +132,7 @@
     storage.start(uriUpdatesB);
 
     storage.finish(uriUpdates);
-    assertContainsExactly(storage, updateB);
+    assertContainsExactly(storage.list(), updateB);
 
     storage.finish(uriUpdatesB);
     assertThat(storage.list()).isEmpty();
@@ -176,7 +177,7 @@
     storage.start(uriUpdatesB);
 
     storage.finish(uriUpdatesA);
-    assertContainsExactly(storage, refUpdateB);
+    assertContainsExactly(storage.list(), refUpdateB);
 
     storage.finish(uriUpdatesB);
     assertThat(storage.list()).isEmpty();
@@ -217,9 +218,9 @@
     assertThat(storage.list()).isEmpty();
   }
 
-  private void assertContainsExactly(
-      ReplicationTasksStorage tasksStorage, ReplicateRefUpdate update) {
-    assertTrue(equals(tasksStorage.list().get(0), update));
+  private void assertContainsExactly(List<ReplicateRefUpdate> all, ReplicateRefUpdate single) {
+    assertThat(all).hasSize(1);
+    assertTrue(equals(all.get(0), single));
   }
 
   private boolean equals(ReplicateRefUpdate one, ReplicateRefUpdate two) {