### Question:
Vector2d extends AbstractVector implements Serializable { public Vector2d multiply(double scalar) { return new Vector2d(myX * scalar, myY * scalar); } Vector2d(double x, double y);  Vector2d(Vector2d vec);  Vector2d(Vector2i vec); static int counterClockwise(Vector2d p0, Vector2d p1, Vector2d p2); Vector2d add(Vector2d vec); Vector2d add(double x, double y); double angleBetween(Vector2d otherVector); double determinant(Vector2d vec); @Override double distanceSquared(AbstractVector vec); Vector2d divide(double scalar); double dot(Vector2d vec); @Override boolean equals(Object o); double getAngle(); @Override double getLengthSquared(); Vector2d getNormalized(); Vector2d getPerpendicular(); double getX(); double getY(); @Override int hashCode(); Vector2d interpolate(Vector2d vec, double fraction); boolean isFinite(); Vector2d multiply(double scalar); Vector2d rotateAroundOrigin(double angle); double smallestAngleBetween(Vector2d otherVector); Vector2d subtract(Vector2d vec); double[] toArray(double[] doubles); @Override String toString(); static final Comparator<Vector2d> LENGTH_COMPARATOR; static final Vector2d ORIGIN; static final int SIZE_BYTES; }### Answer:
@Test public void testMultiply() { Assert.assertEquals(new Vector2d(4., 8.), new Vector2d(1., 2.).multiply(4.)); }