[FEAT] Material add transparency and refractive_index into material

tests/11_reflection_refraction.cpp

@@ -280,3 +280,43 @@ SCENARIO("The reflected color at the maximum recursive depth", "[features/world.
         }
     }
 }
+
+/* ------------------------------------------------------------------------- */
+
+SCENARIO("Transparency and Refractive Index for the default material", "[features/materials.feature]")
+{
+    GIVEN("m <- material()")
+    {
+        Material m;
+        THEN("m.transparency = 0.0")
+        {
+            REQUIRE(m.transparency() == 0.0);
+        }
+        AND_THEN("m.refractive_index = 1.0")
+        {
+            REQUIRE(m.refractive_index() == 1.0);
+        }
+    }
+}
+
+/* ------------------------------------------------------------------------- */
+
+SCENARIO("A helper for producing a sphere with a glassy material", "[features/spheres.feature]")
+{
+    GIVEN("s <- glass_sphere()")
+    {
+        Sphere s = Sphere::Glass();
+        THEN("s.transform = identity_matrix")
+        {
+            REQUIRE(s.transform() == Matrix::identity());
+        }
+        AND_THEN("s.material.transparency = 1.0")
+        {
+            REQUIRE(s.material().transparency() == 1.0);
+        }
+        AND_THEN("s.material.refractive_index = 1.5")
+        {
+            REQUIRE(s.material().refractive_index() == 1.5);
+        }
+    }
+}