Add some tests for BlockRng, BlockRng64 and Xoshiro RNGs (#1639)

Author: AbeZbm

rand_core/src/block.rs

@@ -531,4 +531,33 @@ mod test {
         c[12..].copy_from_slice(&rng3.next_u32().to_le_bytes());
         assert_eq!(b, c);
     }
+
+    #[test]
+    fn blockrng64_generate_and_set() {
+        let mut rng = BlockRng64::<DummyRng64>::from_seed([1, 2, 3, 4, 5, 6, 7, 8]);
+        assert_eq!(rng.index(), rng.results.as_ref().len());
+
+        rng.generate_and_set(5);
+        assert_eq!(rng.index(), 5);
+    }
+
+    #[test]
+    #[should_panic(expected = "index < self.results.as_ref().len()")]
+    fn blockrng64_generate_and_set_panic() {
+        let mut rng = BlockRng64::<DummyRng64>::from_seed([1, 2, 3, 4, 5, 6, 7, 8]);
+        rng.generate_and_set(rng.results.as_ref().len());
+    }
+
+    #[test]
+    fn blockrng_next_u64() {
+        let mut rng = BlockRng::<DummyRng>::from_seed([1, 2, 3, 4]);
+        let result_size = rng.results.as_ref().len();
+        for _i in 0..result_size / 2 - 1 {
+            rng.next_u64();
+        }
+        rng.next_u32();
+
+        let result = rng.next_u64();
+        assert_eq!(rng.index(), 1);
+    }
 }

src/rngs/xoshiro128plusplus.rs

@@ -120,16 +120,19 @@ mod tests {
     }
 
     #[test]
-    fn stable_seed_from_u64() {
+    fn stable_seed_from_u64_and_from_seed() {
         // We don't guarantee value-stability for SmallRng but this
         // could influence keeping stability whenever possible (e.g. after optimizations).
         let mut rng = Xoshiro128PlusPlus::seed_from_u64(0);
+        // from_seed([0; 16]) should produce the same state as seed_from_u64(0).
+        let mut rng_from_seed_0 = Xoshiro128PlusPlus::from_seed([0; 16]);
         let expected = [
             1179900579, 1938959192, 3089844957, 3657088315, 1015453891, 479942911, 3433842246,
             669252886, 3985671746, 2737205563,
         ];
         for &e in &expected {
             assert_eq!(rng.next_u32(), e);
+            assert_eq!(rng_from_seed_0.next_u32(), e);
         }
     }
 }

src/rngs/xoshiro256plusplus.rs

@@ -132,10 +132,12 @@ mod tests {
     }
 
     #[test]
-    fn stable_seed_from_u64() {
+    fn stable_seed_from_u64_and_from_seed() {
         // We don't guarantee value-stability for SmallRng but this
         // could influence keeping stability whenever possible (e.g. after optimizations).
         let mut rng = Xoshiro256PlusPlus::seed_from_u64(0);
+        // from_seed([0; 32]) should produce the same state as seed_from_u64(0).
+        let mut rng_from_seed_0 = Xoshiro256PlusPlus::from_seed([0; 32]);
         let expected = [
             5987356902031041503,
             7051070477665621255,
@@ -150,6 +152,7 @@ mod tests {
         ];
         for &e in &expected {
             assert_eq!(rng.next_u64(), e);
+            assert_eq!(rng_from_seed_0.next_u64(), e);
         }
     }
 }