okhttp-testing-support/src/main/java/com/squareup/okhttp/testing/InstallUncaughtExceptionHandlerListener.java

/*
 * Copyright (C) 2015 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 com.squareup.okhttp.testing;

import org.junit.runner.Description;
import org.junit.runner.Result;
import org.junit.runner.notification.RunListener;

import java.io.PrintWriter;
import java.io.StringWriter;

/**
 * A {@link org.junit.runner.notification.RunListener} used to install an aggressive default
 * {@link java.lang.Thread.UncaughtExceptionHandler} similar to the one found on Android.
 * No exceptions should escape from OkHttp that might cause apps to be killed or tests to fail on
 * Android.
 */
public class InstallUncaughtExceptionHandlerListener extends RunListener {

  private Thread.UncaughtExceptionHandler oldDefaultUncaughtExceptionHandler;
  private Description lastTestStarted;

  @Override public void testRunStarted(Description description) throws Exception {
    System.err.println("Installing aggressive uncaught exception handler");
    oldDefaultUncaughtExceptionHandler = Thread.getDefaultUncaughtExceptionHandler();
    Thread.setDefaultUncaughtExceptionHandler(new Thread.UncaughtExceptionHandler() {
      @Override public void uncaughtException(Thread thread, Throwable throwable) {
        StringWriter errorText = new StringWriter(256);
        errorText.append("Uncaught exception in OkHttp thread \"");
        errorText.append(thread.getName());
        errorText.append("\"\n");
        throwable.printStackTrace(new PrintWriter(errorText));
        errorText.append("\n");
        if (lastTestStarted != null) {
          errorText.append("Last test to start was: ");
          errorText.append(lastTestStarted.getDisplayName());
          errorText.append("\n");
        }
        System.err.print(errorText.toString());
        System.exit(-1);
      }
    });
  }

  @Override public void testStarted(Description description) throws Exception {
    lastTestStarted = description;
  }

  @Override public void testRunFinished(Result result) throws Exception {
    Thread.setDefaultUncaughtExceptionHandler(oldDefaultUncaughtExceptionHandler);
    System.err.println("Uninstalled aggressive uncaught exception handler");
  }
}