void FramesTest::TestWrench2(Wrench& w) {
	// Wrench
	Wrench   w2;	
	CPPUNIT_ASSERT_EQUAL(2*w-w,w);
	CPPUNIT_ASSERT_EQUAL(w*2-w,w);
	CPPUNIT_ASSERT_EQUAL(w+w+w-2*w,w);
	w2=w;
	CPPUNIT_ASSERT_EQUAL(w,w2);
	w2+=w;
	CPPUNIT_ASSERT_EQUAL(2*w,w2);
	w2-=w;
	CPPUNIT_ASSERT_EQUAL(w,w2);
	w.ReverseSign();
	CPPUNIT_ASSERT_EQUAL(w,-w2);
}