YARN-4696. Improving EntityGroupFSTimelineStore on exception handling, test setup, and concurrency.

This commit amends commit d49cfb3504 with a missed test file.

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-timeline-pluginstorage/src/test/java/org/apache/hadoop/yarn/server/timeline/TestOverrideTimelineStoreYarnClient.java

@@ -0,0 +1,56 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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 org.apache.hadoop.yarn.server.timeline;
+
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.yarn.api.records.ApplicationId;
+import org.apache.hadoop.yarn.client.api.YarnClient;
+import org.apache.hadoop.yarn.conf.YarnConfiguration;
+import org.junit.Assert;
+import org.junit.Test;
+
+import java.io.IOException;
+
+public class TestOverrideTimelineStoreYarnClient {
+
+  @Test
+  public void testLifecycleAndOverride() throws Throwable {
+    YarnConfiguration conf = new YarnConfiguration();
+    try(NoRMStore store = new NoRMStore()) {
+      store.init(conf);
+      store.start();
+      Assert.assertEquals(EntityGroupFSTimelineStore.AppState.ACTIVE,
+          store.getAppState(ApplicationId.newInstance(1, 1)));
+      store.stop();
+    }
+  }
+
+  private static class NoRMStore extends EntityGroupFSTimelineStore {
+    @Override
+    protected YarnClient createAndInitYarnClient(Configuration conf) {
+      return null;
+    }
+
+    @Override
+    protected AppState getAppState(ApplicationId appId)
+        throws IOException {
+      return AppState.ACTIVE;
+    }
+  }
+}