### Question:
Vector2D { public void scale(double scaler) { x *= scaler; y *= scaler; } Vector2D(double x, double y); double getX(); double getY(); void translate(Vector2D offset); Vector2D translated(Vector2D offset); void rotate(double angle); Vector2D rotated(double angle); void scale(double scaler); Vector2D scaled(double scaler); Vector2D copy(); @Override int hashCode(); @Override boolean equals(Object obj); @Override String toString();  }### Answer:
@Test void testScaleWithZero() { var vector = new Vector2D(5, 10); vector.scale(0); assertEquals(new Vector2D(0, 0), vector); }
@Test void testScaleWithPositiveNumber() { var vector = new Vector2D(5, 10); vector.scale(5); assertEquals(new Vector2D(25, 50), vector); }
@Test void testScaleWithNegativeNumber() { var vector = new Vector2D(-5, -10); vector.scale(5); assertEquals(new Vector2D(-25, -50), vector); }