Java getDeclaredConstructor fails with NoSuchMethodException from JUnit

I have a base class, which uses reflection to create empty copy of concrete class using the following:

public IBase getEmptyCopy() {
   Class type = this.getClass();
   Constructor<?> ctor;
        try {
            ctor = type.getDeclaredConstructor();
            ctor.setAccessible(true);
            clonedObject =(Base) ctor.newInstance();
        } catch (NoSuchMethodException | SecurityException | InstantiationException | IllegalAccessException | IllegalArgumentException | InvocationTargetException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
}
}

I've created a class called Test with the following main method:

public class Test {
    public static void main(String [] args)  {
....
ConcreteClass emptyInstance = (ConcreteClass) someInstance.getEmptyCopy();
}

All seem to work, however when I try to do the same in a JUnit test case:

@Test   
   public void test() {
    ....
        ConcreteClass emptyInstance = (ConcreteClass) someInstance.getEmptyCopy();
        }

I get an java.lang.NoSuchMethodException on the getDeclaredConstructor call.

can anyone explain what is the reason for that?

Thanks.