测试 Lombok 的 @UtilityClass 自动生成的代码

Question

I have a class that's annotated with @UtilityClass like this

@UtilityClass
public class myUtilClass {
...
}

JaCoCo doesn't give me full coverage for this class because of the auto-generated code created by the annotation @UtilityClass . Ideally, I do not want to change any config files to ignore auto-gen code. How can this code be tested?

Answer 1

The only "coverable" code that is generated by @UtilityClass is in the constructor:

private MyUtilClass() {
    throw new UnsupportedOperationException("This is a utility class and cannot be instantiated");
}

As this is a private constructor that never should be called, you cannot test it regularly.

If you really want to call it, you can do it with some ugly reflective code:

Constructor<MyUtilClass> constructor;
constructor = MyUtilClass.class.getDeclaredConstructor();
constructor.setAccessible(true);
constructor.newInstance();

But you should not do this just for the sake of coverage. Having a high coverage is generally a good idea, but not if you have to sacrifice good testing standards.

I suggest you advice JaCoCo to ignore Lombok's code by adding this line to your lombok.config file:

lombok.addLombokGeneratedAnnotation = true

You don't have to configure this for your whole project. If you put this file only into the package of MyUtilClass , JaCoCo will only ignore generated code in this package.

Answer 2

Just write this unit test to ensure your class cannot be instantiated because of @UtilityClass annotation. Then, coverage will be OK.

@Test
  void test_cannot_instantiate() {
    assertThrows(InvocationTargetException.class, () -> {
      var constructor = YOUR_CLASS_NAME.class.getDeclaredConstructor();
      assertTrue(Modifier.isPrivate(constructor.getModifiers()));
      constructor.setAccessible(true);
      constructor.newInstance();
    });
  }