public void TestOverlap(int a1, int a2, int b1, int b2, int expected)
        {
            var l1 = new LineSegment1D(FixedPoint.FromInt(a1), FixedPoint.FromInt(a2));
            var l2 = new LineSegment1D(FixedPoint.FromInt(b1), FixedPoint.FromInt(b2));

            var overlap1    = l1.MeasureOverlap(l2);
            var overlapInt1 = (int)overlap1;

            Assert.Equal(expected, overlapInt1);

            var overlap2    = l2.MeasureOverlap(l1);
            var overlapInt2 = (int)overlap2;

            Assert.Equal(expected, overlapInt2);
        }