Add property-based test for k_smallest when applied to ranges

Author: nicoonoclaste

tests/test_std.rs

@@ -1,4 +1,6 @@
 use permutohedron;
+use quickcheck::quickcheck;
+use std::cmp::min;
 use itertools as it;
 use crate::it::Itertools;
 use crate::it::ExactlyOneError;
@@ -354,6 +356,18 @@ fn sorted_by() {
     it::assert_equal(v, vec![4, 3, 2, 1, 0]);
 }
 
+quickcheck! {
+    fn k_smallest_range(n: u64, m: u64, k: u64) -> () {
+        // Check that taking the k smallest elements in n..n+m
+        //  yields n..n+min(k, m)
+        let i = (n..n.saturating_add(m)).into_iter();
+        it::assert_equal(
+            i.k_smallest(k as usize),
+            n..n.saturating_add(min(k, m))
+        );
+    }
+}
+
 #[test]
 fn sorted_by_key() {
     let sc = [3, 4, 1, 2].iter().cloned().sorted_by_key(|&x| x);