Mock final new instance created?

Question

How to mock private final MockClass mockClass = new MockClass();

 public class SimpleClass {
     private final MockClass mockClass = new MockClass();
 }

Answer 1

Use dependency injection; then you can have whatever you want in the field:

class SimpleClass {
  private final MockClass mockClass;

  SimpleClass(MockClass mockClass) {
    this.mockClass = mockClass;
  }
}

See Misko Hevery's guide to writing testable code : your code is an example of the warning sign "new keyword in a constructor or at field declaration".