'horizontal');
          c1.classList.add('flex');
          c2.classList.add('flex-2');
          c3.classList.add('flex-3');
          assert.isTrue(positionEquals(container, 0, 50, 0, 300), "container position ok");
          // |c1| | c2 | |  c3  |
          assert.isTrue(positionEquals(c1, 0, 50, 0, 50), "child 1 position ok");
          assert.isTrue(positionEquals(c2, 0, 50, 50, 150), "child 2 position ok");
          assert.isTrue(positionEquals(c3, 0, 50, 150, 300), "child 3 position ok");
        