public void ComputeNormals()
        {
            var builder = new MeshBuilder(false);
            builder.AddPolygon(new List<Vector3>
                {
                    new Vector3(0f, 0f, 0f),
                    new Vector3(7f, 0f, 0f),
                    new Vector3(7f, 0f, 7f),
                });

            Assert.IsNull(builder.Normals);
            Assert.IsFalse(builder.HasNormals);

            builder.ComputeNormalsAndTangents(MeshFaces.Default);

            Assert.IsTrue(builder.HasNormals);
            Assert.AreEqual(3, builder.Normals.Count);
        }