boolean touches(Bubble b) {
    //distance between them is greater than sum of radii (both sides of equation squared)
    return (this.coordinateX - b.coordinateX) * (this.coordinateX - b.coordinateX)
        + (this.coordinateY - b.coordinateY) * (this.coordinateY - b.coordinateY)
        <= (this.radius + b.radius) * (this.radius + b.radius);
  }
@Test
  void touchesTest() {
    var b1 = new Bubble(0, 0, 1, 2);
    var b2 = new Bubble(1, 1, 2, 1);
    var b3 = new Bubble(10, 10, 3, 1);
    //b1 touches b2 but not b3
    assertTrue(b1.touches(b2));
    assertFalse(b1.touches(b3));
  }