Added a SchedulerMock to be used for unit tests

Original commit: elastic/x-pack-elasticsearch@d4dfb37431

src/test/java/org/elasticsearch/alerts/scheduler/SchedulerMock.java

@@ -0,0 +1,55 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License;
+ * you may not use this file except in compliance with the Elastic License.
+ */
+package org.elasticsearch.alerts.scheduler;
+
+import org.elasticsearch.common.joda.time.DateTime;
+
+import java.util.Collection;
+import java.util.List;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.ConcurrentMap;
+import java.util.concurrent.CopyOnWriteArrayList;
+
+/**
+ * A mock scheduler to help with unit testing. Provide {@link SchedulerMock#fire} method to manually trigger
+ * jobs.
+ */
+public class SchedulerMock implements Scheduler {
+
+    private final List<Listener> listeners = new CopyOnWriteArrayList<>();
+
+    private final ConcurrentMap<String, Job> jobs = new ConcurrentHashMap<>();
+
+    @Override
+    public void start(Collection<? extends Job> jobs) {
+    }
+
+    @Override
+    public void stop() {
+    }
+
+    @Override
+    public void add(Job job) {
+        jobs.put(job.name(), job);
+    }
+
+    @Override
+    public boolean remove(String jobName) {
+        return jobs.remove(jobName) != null;
+    }
+
+    @Override
+    public void addListener(Listener listener) {
+        listeners.add(listener);
+    }
+
+    public void fire(String jobName) {
+        DateTime now = new DateTime();
+        for (Listener listener : listeners) {
+            listener.fire(jobName, now ,now);
+        }
+    }
+}