Add a test for vec::retain

Author: sanxiyn

src/libcore/vec.rs

@@ -2799,6 +2799,13 @@ mod tests {
         assert filter(~[1u, 2u, 4u, 8u, 16u], is_three) == ~[];
     }
 
+    #[test]
+    fn test_retain() {
+        let mut v = ~[1, 2, 3, 4, 5];
+        v.retain(is_odd);
+        assert v == ~[1, 3, 5];
+    }
+
     #[test]
     fn test_foldl() {
         // Test on-stack fold.