Pcg64Si unit tests

src/pcg64si.rs

@@ -43,3 +43,41 @@ impl SeedableRng for Pcg64Si {
         }
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::collections::HashSet;
+
+    // For a given seed the RNG is deterministic
+    // thus we can perform some basic tests consistently
+    #[test]
+    fn test_rng_next() {
+        let mut rng = Pcg64Si::from_seed([1, 2, 3, 4, 5, 6, 7, 8]);
+        let mut values_set: HashSet<u32> = HashSet::new();
+        // Generate 1000 values modulus 100 (so each value is between 0 and 99)
+        for _ in 0..1000 {
+            values_set.insert(rng.next_u32() % 100);
+        }
+        // Expect to generate every number between 0 and 99 (the generated values are somewhat evenly distributed)
+        assert_eq!(values_set.len(), 100);
+    }
+
+    #[test]
+    fn test_rng_from_seed() {
+        // Different seeds should result in a different RNG state
+        let rng1 = Pcg64Si::from_seed([1, 2, 3, 4, 5, 6, 7, 8]);
+        let rng2 = Pcg64Si::from_seed([1, 2, 3, 4, 5, 6, 7, 7]);
+        assert_ne!(rng1.state, rng2.state);
+    }
+
+    #[test]
+    fn test_rng_fill_bytes() {
+        // This uses the next_u64/u32 functions underneath, so don't need to test the pseudo randomness again
+        let mut array: [u8; 8] = [0, 0, 0, 0, 0, 0, 0, 0];
+        let mut rng = Pcg64Si::from_seed([1, 2, 3, 4, 5, 6, 7, 8]);
+        let result = rng.try_fill_bytes(&mut array);
+        assert!(result.is_ok());
+        assert_ne!(array, [0, 0, 0, 0, 0, 0, 0, 0]);
+    }
+}