Merge branch 'shuffle_underflow' into genesis

beacon_chain/utils/vec_shuffle/src/lib.rs

@@ -25,10 +25,16 @@ pub fn shuffle<T>(
     -> Result<Vec<T>, ShuffleErr>
 {
     let mut rng = ShuffleRng::new(seed);
+
     if list.len() > rng.rand_max as usize {
         return Err(ShuffleErr::ExceedsListLength);
     }
-    for i in 0..(list.len() - 1) {
+
+    if list.is_empty() {
+        return Ok(list);
+    }
+
+    for i in 0..(list.len().saturating_sub(1)) {
         let n = list.len() - i;
         let j = rng.rand_range(n as u32) as usize + i;
         list.swap(i, j);
@@ -39,17 +45,40 @@ pub fn shuffle<T>(
 
 #[cfg(test)]
 mod tests {
+    extern crate yaml_rust;
+
     use super::*;
     use super::hashing::canonical_hash;
+    use std::fs::File;
+    use std::io::prelude::*;
+    use self::yaml_rust::yaml;
 
     #[test]
     fn test_shuffling() {
-        let seed = canonical_hash(b"4kn4driuctg8");
-        let list: Vec<usize> = (0..12).collect();
-        let s = shuffle(&seed, list).unwrap();
-        assert_eq!(
-            s,
-            vec![7, 3, 2, 5, 11, 9, 1, 0, 4, 6, 10, 8],
-        )
+        let mut file = File::open("./src/specs/shuffle_test_vectors.yaml").unwrap();
+        let mut yaml_str = String::new();
+
+        file.read_to_string(&mut yaml_str).unwrap();
+
+        let docs = yaml::YamlLoader::load_from_str(&yaml_str).unwrap();
+        let doc = &docs[0];
+        let test_cases = doc["test_cases"].as_vec();
+
+        for test_case in test_cases.unwrap() {
+            let input = test_case["input"].clone().into_vec().unwrap();
+            let output = test_case["output"].clone().into_vec().unwrap();
+            let seed_bytes = test_case["seed"].as_str().unwrap().as_bytes();
+            let mut seed;
+
+            if seed_bytes.len() > 0 {
+                seed = canonical_hash(seed_bytes);
+            } else {
+                seed = vec![];
+            }
+
+            let mut s = shuffle(&seed, input).unwrap();
+
+            assert_eq!(s, output);
+        }
     }
 }