world: add test_world constructor for book tests.

rtchallenge/src/world.rs

@@ -1,4 +1,10 @@
-use crate::{lights::PointLight, spheres::Sphere};
+use crate::{
+    lights::PointLight,
+    materials::Material,
+    matrices::{Matrix2x2, Matrix4x4},
+    spheres::Sphere,
+    tuples::{Color, Tuple},
+};
 
 /// World holds all drawable objects and the light(s) that illuminate them.
 ///
@@ -17,3 +23,32 @@ pub struct World {
     pub light: Option<PointLight>,
     pub objects: Vec<Sphere>,
 }
+
+impl World {
+    /// Creates a world suitable for use across multiple tests in from the book.
+    ///
+    /// # Examples
+    /// ```
+    /// use rtchallenge::world::World;
+    ///
+    /// let w = World::test_world();
+    /// assert_eq!(w.objects.len(), 2);
+    /// assert!(w.light.is_some());
+    /// ```
+    pub fn test_world() -> World {
+        let light = PointLight::new(Tuple::point(-10., 10., -10.), Color::new(1., 1., 1.));
+        let mut s1 = Sphere::default();
+        s1.material = Material {
+            color: Color::new(0.8, 1., 0.6),
+            diffuse: 0.7,
+            specular: 0.2,
+            ..Material::default()
+        };
+        let mut s2 = Sphere::default();
+        s2.transform = Matrix4x4::scaling(0.5, 0.5, 0.5);
+        World {
+            light: Some(light),
+            objects: vec![s1, s2],
+        }
+    }
+}