Use a TestRule to check for connection leaks

okhttp-testing-support/src/main/java/okhttp3/OkHttpClientTestingRule.java

@@ -0,0 +1,43 @@
+/*
+ * Copyright (C) 2019 Square, Inc.
+ *
+ * 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 okhttp3;
+
+import org.junit.rules.TestRule;
+import org.junit.runner.Description;
+import org.junit.runners.model.Statement;
+
+import static okhttp3.TestUtil.defaultClient;
+
+public class OkHttpClientTestingRule implements TestRule {
+  public OkHttpClient client = defaultClient();
+
+  @Override
+  public Statement apply(Statement base, Description description) {
+    return statement(base);
+  }
+
+  private Statement statement(final Statement base) {
+    return new Statement() {
+      public void evaluate() throws Throwable {
+        try {
+          base.evaluate();
+        } finally {
+          TestUtil.ensureAllConnectionsReleased(client);
+        }
+      }
+    };
+  }
+}