[FEAT] Finish the Chapter 05 with the render of a sphere shadow.

tests/05_rays.cpp

@@ -459,6 +459,10 @@ SCENARIO("The hit is always the lowest nonnegative intersection", "[features/int
                                 {
                                     REQUIRE(i == i4);
                                 }
+                                AND_THEN("i is defined")
+                                {
+                                    REQUIRE(i.is_defined());
+                                }
                             }
                         }
                     }