### Question:
Vector2D { public Vector2D scaled(double scaler) { Vector2D vector = copy(); vector.scale(scaler); return vector; } 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 testScaledWithZero() { assertEquals(new Vector2D(0, 0), new Vector2D(5, 10).scaled(0)); }
@Test void testScaledWithPositiveNumber() { assertEquals(new Vector2D(25, 50), new Vector2D(5, 10).scaled(5)); }
@Test void testScaledWithNegativeNumber() { assertEquals(new Vector2D(-25, -50), new Vector2D(5, 10).scaled(-5)); }