### Question:
Vector2 extends AVector2 { public Vector2 normalize() { if (!isZeroVector()) { final double length = getLength2(); x /= length; y /= length; } return this; } protected  Vector2(); protected  Vector2(final double x, final double y); protected  Vector2(final IVector original); static Vector2 zero(); static Vector2 fromX(final double x); static Vector2 fromY(final double y); static Vector2 fromXY(final double x, final double y); static Vector2 fromAngle(final double angle); static Vector2 fromAngleLength(final double angle, final double length); static Vector2 fromPoints(final IVector2 start, final IVector2 end); static Vector2 copy(final IVector original); static Vector2 fromReal(final RealVector vector); @Override Vector2 copy(); Vector2 set(final IVector original); Vector2 setX(final double x); Vector2 setY(final double y); void set(final int i, final double value); Vector2 add(final IVector vector); Vector2 subtract(final IVector vector); Vector2 multiply(final double factor); Vector2 scaleTo(final double newLength); Vector2 turn(final double angle); Vector2 turnTo(final double angle); Vector2 normalize(); @Override Vector2 getXYVector(); @Override double x(); @Override double y();  }### Answer:
@Test public void testNormalize() { assertThat(Vector2.fromXY(42, 1337).normalize().getLength2()).isCloseTo(1, within(1e-6)); assertThat(Vector2.fromXY(42, 1337).normalizeNew().getLength2()).isCloseTo(1, within(1e-6)); assertThat(Vector2.zero().normalize().getLength2()).isCloseTo(0, within(1e-6)); assertThat(Vector2.zero().normalizeNew().getLength2()).isCloseTo(0, within(1e-6)); }