Added a test for 4 vs 4.

src/lib.rs

@@ -411,4 +411,47 @@ mod tests {
             assert_relative_eq!(rating, expected, epsilon = EPSILON);
         }
     }
+
+    #[test]
+    fn test_rate_4vs4() {
+        let _ = env_logger::try_init();
+
+        let alice = Rating::new(MU, SIGMA);
+        let bob = Rating::new(MU, SIGMA);
+        let chris = Rating::new(MU, SIGMA);
+        let darren = Rating::new(MU, SIGMA);
+        let eric = Rating::new(MU, SIGMA);
+        let fred = Rating::new(MU, SIGMA);
+        let grace = Rating::new(MU, SIGMA);
+        let laura = Rating::new(MU, SIGMA);
+
+        let expected_ratings = vec![
+            Rating::new(27.19791584649575, 8.058911711843994),
+            Rating::new(27.19791584649575, 8.058911711843994),
+            Rating::new(27.19791584649575, 8.058911711843994),
+            Rating::new(27.19791584649575, 8.058911711843994),
+            Rating::new(22.802084153504236, 8.058911711843994),
+            Rating::new(22.802084153504236, 8.058911711843994),
+            Rating::new(22.802084153504236, 8.058911711843994),
+            Rating::new(22.802084153504236, 8.058911711843994),
+        ];
+
+        let ratings = rate(
+            &[
+                (alice, 0),
+                (bob, 0),
+                (chris, 0),
+                (darren, 0),
+                (eric, 1),
+                (fred, 1),
+                (grace, 1),
+                (laura, 1),
+            ],
+            &[0, 1],
+        );
+
+        for (rating, expected) in ratings.iter().zip(expected_ratings.iter()) {
+            assert_relative_eq!(rating, expected, epsilon = EPSILON);
+        }
+    }
 }