JaCoCo and missed coverage of private default constructor

Question

I'd like to see an example to prevent JaCoCo to report private empty constructors as non-covered code in a Java class.

In the maven plugin configuration I have

   <rule>
     <element>CLASS</element>
       <excludes>
         <exclude>JAVAC.SYNTHCLASS</exclude>
         <exclude>JAVAC.SYNTHMETH</exclude>
       </excludes>
     </element>
   </rule>

Isn't there something similar for the constructor?

Answer 1

For this use case, reflection is perfectly acceptable, there are few and well known classes. The bellow code could be used with an automatic class detection based on the name. For sample ".*Factory" classes with additional asserts.

@Test
public void testCoverage()
    throws SecurityException, NoSuchMethodException, InstantiationException, IllegalAccessException, InvocationTargetException {
    coverageSingleton(MySingleton1.class);
    coverageSingleton(MySingleton2.class);
}

private <S> void coverageSingleton(Class<S> singletonClass)
    throws SecurityException, NoSuchMethodException, InstantiationException, IllegalAccessException, InvocationTargetException {
    final Constructor<S> constructor = singletonClass.getDeclaredConstructor();
    constructor.setAccessible(true);
    constructor.newInstance();
}