public void test_Envelope()
        {
            //create a new collection
            MultiLineString multiLS = CreateMLS();

            //put the envelope into a geometry
            Geometry env = multiLS.GetEnvelope() as Geometry;

            //make sure there is something in the envelope
            Assertion.AssertEquals("Envelope-1: ", false, env.IsEmpty());

            Coordinates coords = env.GetCoordinates();

            //check the first set of coordinates (minX, minY)
            Assertion.AssertEquals("Envelope-2: ", 0.0, coords[0].X);
            Assertion.AssertEquals("Envelope-3: ", 5.0, coords[0].Y);

            //check the second set of coordinates (maxX, minY)
            Assertion.AssertEquals("Envelope-4: ", 18.0, coords[1].X);
            Assertion.AssertEquals("Envelope-5: ", 5.0, coords[1].Y);

            //check the third set of coordinates (maxX, maxY)
            Assertion.AssertEquals("Envelope-6: ", 18.0, coords[2].X);
            Assertion.AssertEquals("Envelope-7: ", 23.0, coords[2].Y);

            //check the forth set of coordinates (minX, maxY)
            Assertion.AssertEquals("Envelope-8: ", 0.0, coords[3].X);
            Assertion.AssertEquals("Envelope-9: ", 23.0, coords[3].Y);

            //check the fifth set of coordinates (minX, minY)
            Assertion.AssertEquals("Envelope-10: ", 0.0, coords[4].X);
            Assertion.AssertEquals("Envelope-11: ", 5.0, coords[4].Y);

            //create a null collection
            GeometryFactory gf = new GeometryFactory(_precMod, _sRID);

            multiLS = gf.CreateMultiLineString(null);

            //put the envelope into a geometry
            env = multiLS.GetEnvelope() as Geometry;

            //make sure there is something in the envelope
            Assertion.AssertEquals("Envelope-12: ", true, env.IsEmpty());
        }