Introduce SettableWatcher to make writing Watcher related integration…

… test more easily

testing/common/src/main/java/com/linecorp/centraldogma/testing/SettableWatcher.java

@@ -0,0 +1,76 @@
+/*
+ * Copyright 2022 LINE Corporation
+ *
+ * LINE Corporation 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:
+ *
+ *   https://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.linecorp.centraldogma.testing;
+
+import java.util.List;
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.CopyOnWriteArrayList;
+import java.util.concurrent.Executor;
+import java.util.concurrent.ScheduledExecutorService;
+import java.util.function.BiConsumer;
+
+import com.linecorp.armeria.common.CommonPools;
+import com.linecorp.centraldogma.client.Latest;
+import com.linecorp.centraldogma.client.Watcher;
+import com.linecorp.centraldogma.common.Revision;
+
+public final class SettableWatcher<T> implements Watcher<T> {
+    private volatile T value;
+    private final List<BiConsumer<? super Revision, ? super T>> updateListeners = new CopyOnWriteArrayList<>();
+
+    @Override
+    public ScheduledExecutorService watchScheduler() {
+        return CommonPools.blockingTaskExecutor();
+    }
+
+    @Override
+    public CompletableFuture<Latest<T>> initialValueFuture() {
+        return CompletableFuture.completedFuture(latest());
+    }
+
+    @Override
+    public Latest<T> latest() {
+        return new Latest<>(Revision.HEAD, value);
+    }
+
+    @Override
+    public void close() {
+        updateListeners.clear();
+    }
+
+    public void setValue(T value) {
+        this.value = value;
+        if (this.value != null) {
+            for (BiConsumer<? super Revision, ? super T> l : updateListeners) {
+                l.accept(Revision.HEAD, value);
+            }
+        }
+    }
+
+    @Override
+    public void watch(BiConsumer<? super Revision, ? super T> listener) {
+        updateListeners.add(listener);
+        if (value != null) {
+            listener.accept(Revision.HEAD, value);
+        }
+    }
+
+    @Override
+    public void watch(BiConsumer<? super Revision, ? super T> listener, Executor executor) {
+        watch(listener);
+    }
+}

testing/common/src/main/java/com/linecorp/centraldogma/testing/package-info.java

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+/*
+ * Copyright 2022 LINE Corporation
+ *
+ * LINE Corporation 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:
+ *
+ *   https://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.
+ */
+
+/**
+ * Simplifies the integration testing with Central Dogma.
+ */
+@NonNullByDefault
+package com.linecorp.centraldogma.testing;
+
+import com.linecorp.centraldogma.common.util.NonNullByDefault;