class Test {
  public foo: string;
  private quux: string;
  // ... 
}   

class Plop {
  public bar: string;
  // ...
}

class TestPlopMixin implements Test, Plop {
  public foo: string;
  public bar: string;
  private quux: string;
  // Class TestPlopMixin incorrectly implements interface Test
  // Types have separate declarations of a private property 'quux'
}