@Test public void twiceWillReturnDoubleTheInput() { int actual = doubler.twice(HALF); int expected = WHOLE; assertThat(actual).isEqualTo(expected); }
int twice(int x) { return adder.add(x, x); }
Doubler { int twice(int x) { return adder.add(x, x); } }
Doubler { int twice(int x) { return adder.add(x, x); } Doubler(Adder adder); }
Doubler { int twice(int x) { return adder.add(x, x); } Doubler(Adder adder);  }
Doubler { int twice(int x) { return adder.add(x, x); } Doubler(Adder adder);   }