### Question:
Angle extends AAngularMeasure implements IAngle { @Override public IAngle multiply(final double factor) { return new Angle(this.angle * factor); } private  Angle(); private  Angle(double rad); static Angle zero(); static Angle ofRad(double rad); static Angle ofDeg(double deg); static Angle ofRotation(double turns); static Angle ofVec(IVector2 vector); static Angle ofAngularMeasure(IAngularMeasure angularMeasure); @Override IAngle add(final IAngularMeasure angle); @Override IAngle add(final double angle); @Override IAngle subtract(final IAngularMeasure angle); @Override IAngle subtract(final double angle); @Override IAngle multiply(final double factor);  }### Answer:
@Test public void multiply() { assertEquals(0, Angle.zero().multiply(Math.PI / 2).multiply(42).asRad(), ACCURACY); assertEquals(42, Angle.ofDeg(21).multiply(1).multiply(2).asDeg(), ACCURACY); }