1 files changed, 11 insertions, 3 deletions
diff --git a/tests/lang/lib.nix b/tests/lang/lib.nix
index f888453ff..ec705299a 100644
--- a/tests/lang/lib.nix
+++ b/tests/lang/lib.nix
@@ -1,18 +1,26 @@
+with builtins;
+
 rec {
 
   fold = op: nul: list:
     if list == []
     then nul
-    else op (builtins.head list) (fold op nul (builtins.tail list));
+    else op (head list) (fold op nul (tail list));
 
   concat =
     fold (x: y: x + y) "";
 
   flatten = x:
-    if builtins.isList x
+    if isList x
     then fold (x: y: (flatten x) ++ y) [] x
     else [x];
 
-  sum = fold (x: y: builtins.add x y) 0;
+  sum = fold (x: y: add x y) 0;
+
+  hasSuffix = ext: fileName:
+    let lenFileName = stringLength fileName;
+        lenExt = stringLength ext;
+    in !(lessThan lenFileName lenExt) &&
+       substring (sub lenFileName lenExt) lenFileName fileName == ext;
 
 }