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

Author: AbeZbm

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);
+    }
 }