How to add test coverage to a private constructor?

Question

This is the code:

package com.XXX;
public final class Foo {
  private Foo() {
    // intentionally empty
  }
  public static int bar() {
    return 1;
  }
}

This is the test:

package com.XXX;
public FooTest {
  @Test 
  void testValidatesThatBarWorks() {
    int result = Foo.bar();
    assertEquals(1, result);
  }
  @Test(expected = java.lang.IllegalAccessException.class)
  void testValidatesThatClassFooIsNotInstantiable() {
    Class cls = Class.forName("com.XXX.Foo");
    cls.newInstance(); // exception here
  }
}

Works fine, the class is tested. But Cobertura says that there is zero code coverage of the private constructor of the class. How can we add test coverage to such a private constructor?

Answer 1

Well, there are ways you could potentially use reflection etc - but is it really worth it? This is a constructor which should never be called, right?

If there's an annotation or anything similar that you can add to the class to make Cobertura understand that it won't be called, do that: I don't think it's worth going through hoops to add coverage artificially.

EDIT: If there's no way of doing it, just live with the slightly reduced coverage. Remember that coverage is meant to be something which is useful to you - you should be in charge of the tool, not the other way round.