@Test public void test_no_book() { assertThat(calculator.price()).isEqualTo(0); }
public double price(int... books) { return 0.0; }
BookPriceCalculator { public double price(int... books) { return 0.0; } }
BookPriceCalculator { public double price(int... books) { return 0.0; }  }
BookPriceCalculator { public double price(int... books) { return 0.0; }  double price(int... books); }
BookPriceCalculator { public double price(int... books) { return 0.0; }  double price(int... books);  }