使用不同的类加载器进行不同的JUnit测试？

时间：2008-09-03 16:45:00

标签： java unit-testing junit singleton

我有一个Singleton / Factory对象，我想为其编写一个JUnit测试。 Factory方法根据类路径上属性文件中的类名决定实例化哪个实现类。如果未找到属性文件，或者属性文件不包含classname键，则该类将实例化默认实现类。

由于工厂在实例化后保持Singleton的静态实例使用，为了能够在Factory方法中测试“故障转移”逻辑，我需要在不同的类加载器中运行每个测试方法。

使用JUnit（或其他单元测试包）有没有办法做到这一点？

编辑：这是一些正在使用的工厂代码：

private static MyClass myClassImpl = instantiateMyClass();

private static MyClass instantiateMyClass() {
    MyClass newMyClass = null;
    String className = null;

    try {
        Properties props = getProperties();
        className = props.getProperty(PROPERTY_CLASSNAME_KEY);

        if (className == null) {
            log.warn("instantiateMyClass: Property [" + PROPERTY_CLASSNAME_KEY
                    + "] not found in properties, using default MyClass class [" + DEFAULT_CLASSNAME + "]");
            className = DEFAULT_CLASSNAME;
        }

        Class MyClassClass = Class.forName(className);
        Object MyClassObj = MyClassClass.newInstance();
        if (MyClassObj instanceof MyClass) {
            newMyClass = (MyClass) MyClassObj;
        }
    }
    catch (...) {
        ...
    }

    return newMyClass;
}

private static Properties getProperties() throws IOException {

    Properties props = new Properties();

    InputStream stream = Thread.currentThread().getContextClassLoader().getResourceAsStream(PROPERTIES_FILENAME);

    if (stream != null) {
        props.load(stream);
    }
    else {
        log.error("getProperties: could not load properties file [" + PROPERTIES_FILENAME + "] from classpath, file not found");
    }

    return props;
}

5 个答案:

答案 0 :(得分：37)

这个问题可能已经过时了，但因为这是我遇到这个问题时最接近的答案，但我会描述我的解决方案。

使用JUnit 4

拆分你的测试，以便每个类有一个测试方法（这个解决方案只更改类之间的类加载器，而不是方法之间，因为父类运行器每个类收集一次所有方法）

将@RunWith(SeparateClassloaderTestRunner.class)注释添加到测试类中。

创建SeparateClassloaderTestRunner，如下所示：

public class SeparateClassloaderTestRunner extends BlockJUnit4ClassRunner {

    public SeparateClassloaderTestRunner(Class<?> clazz) throws InitializationError {
        super(getFromTestClassloader(clazz));
    }

    private static Class<?> getFromTestClassloader(Class<?> clazz) throws InitializationError {
        try {
            ClassLoader testClassLoader = new TestClassLoader();
            return Class.forName(clazz.getName(), true, testClassLoader);
        } catch (ClassNotFoundException e) {
            throw new InitializationError(e);
        }
    }

    public static class TestClassLoader extends URLClassLoader {
        public TestClassLoader() {
            super(((URLClassLoader)getSystemClassLoader()).getURLs());
        }

        @Override
        public Class<?> loadClass(String name) throws ClassNotFoundException {
            if (name.startsWith("org.mypackages.")) {
                return super.findClass(name);
            }
            return super.loadClass(name);
        }
    }
}

注意我必须这样做才能测试在遗留框架中运行的代码，我无法更改。鉴于选择，我会减少使用静态和/或放入测试挂钩以允许系统重置。它可能不是很漂亮，但它允许我测试很多代码，否则很难。

此解决方案还会破坏依赖于类加载技巧的其他任何东西，例如Mockito。

答案 1 :(得分：3)

当我遇到这种情况时，我更喜欢使用什么是一个黑客。我可能会反而暴露一个受保护的方法，例如reinitialize（），然后从测试中调用它来有效地将工厂设置回其初始状态。此方法仅适用于测试用例，我将其记录为原样。

这有点像黑客，但它比其他选项容易得多，你不需要第三方库来做（虽然如果你更喜欢更清洁的解决方案，可能还有某种第三方工具在那里你可以使用）。

答案 2 :(得分：3)

您可以通过再次调用myClassImpl来使用反射来设置instantiateMyClass()。查看this answer以查看用于处理私有方法和变量的示例模式。

答案 3 :(得分：2)

如果通过Ant task执行Junit，您可以设置 fork=true 来执行其自己的JVM中的每一类测试。同时将每个测试方法放在自己的类中，每个测试方法都会加载并初始化自己的MyClass版本。这是极端但非常有效的。

答案 4 :(得分：0)

下面你可以找到一个不需要单独的JUnit测试运行器的样本，也可以使用Mockito等类加载技巧。

package com.mycompany.app;

import static org.junit.Assert.assertEquals;
import static org.mockito.Mockito.mock;
import static org.mockito.Mockito.verify;

import java.net.URLClassLoader;

import org.junit.Test;

public class ApplicationInSeparateClassLoaderTest {

  @Test
  public void testApplicationInSeparateClassLoader1() throws Exception {
    testApplicationInSeparateClassLoader();
  }

  @Test
  public void testApplicationInSeparateClassLoader2() throws Exception {
    testApplicationInSeparateClassLoader();
  }

  private void testApplicationInSeparateClassLoader() throws Exception {
    //run application code in separate class loader in order to isolate static state between test runs
    Runnable runnable = mock(Runnable.class);
    //set up your mock object expectations here, if needed
    InterfaceToApplicationDependentCode tester = makeCodeToRunInSeparateClassLoader(
        "com.mycompany.app", InterfaceToApplicationDependentCode.class, CodeToRunInApplicationClassLoader.class);
    //if you want to try the code without class loader isolation, comment out above line and comment in the line below
    //CodeToRunInApplicationClassLoader tester = new CodeToRunInApplicationClassLoaderImpl();
    tester.testTheCode(runnable);
    verify(runnable).run();
    assertEquals("should be one invocation!", 1, tester.getNumOfInvocations());
  }

  /**
   * Create a new class loader for loading application-dependent code and return an instance of that.
   */
  @SuppressWarnings("unchecked")
  private <I, T> I makeCodeToRunInSeparateClassLoader(
      String packageName, Class<I> testCodeInterfaceClass, Class<T> testCodeImplClass) throws Exception {
    TestApplicationClassLoader cl = new TestApplicationClassLoader(
        packageName, getClass(), testCodeInterfaceClass);
    Class<?> testerClass = cl.loadClass(testCodeImplClass.getName());
    return (I) testerClass.newInstance();
  }

  /**
   * Bridge interface, implemented by code that should be run in application class loader.
   * This interface is loaded by the same class loader as the unit test class, so
   * we can call the application-dependent code without need for reflection.
   */
  public static interface InterfaceToApplicationDependentCode {
    void testTheCode(Runnable run);
    int getNumOfInvocations();
  }

  /**
   * Test-specific code to call application-dependent code. This class is loaded by 
   * the same class loader as the application code.
   */
  public static class CodeToRunInApplicationClassLoader implements InterfaceToApplicationDependentCode {
    private static int numOfInvocations = 0;

    @Override
    public void testTheCode(Runnable runnable) {
      numOfInvocations++;
      runnable.run();
    }

    @Override
    public int getNumOfInvocations() {
      return numOfInvocations;
    }
  }

  /**
   * Loads application classes in separate class loader from test classes.
   */
  private static class TestApplicationClassLoader extends URLClassLoader {

    private final String appPackage;
    private final String mainTestClassName;
    private final String[] testSupportClassNames;

    public TestApplicationClassLoader(String appPackage, Class<?> mainTestClass, Class<?>... testSupportClasses) {
      super(((URLClassLoader) getSystemClassLoader()).getURLs());
      this.appPackage = appPackage;
      this.mainTestClassName = mainTestClass.getName();
      this.testSupportClassNames = convertClassesToStrings(testSupportClasses);
    }

    private String[] convertClassesToStrings(Class<?>[] classes) {
      String[] results = new String[classes.length];
      for (int i = 0; i < classes.length; i++) {
        results[i] = classes[i].getName();
      }
      return results;
    }

    @Override
    public Class<?> loadClass(String className) throws ClassNotFoundException {
      if (isApplicationClass(className)) {
        //look for class only in local class loader
        return super.findClass(className);
      }
      //look for class in parent class loader first and only then in local class loader
      return super.loadClass(className);
    }

    private boolean isApplicationClass(String className) {
      if (mainTestClassName.equals(className)) {
        return false;
      }
      for (int i = 0; i < testSupportClassNames.length; i++) {
        if (testSupportClassNames[i].equals(className)) {
          return false;
        }
      }
      return className.startsWith(appPackage);
    }

  }

}
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