1 files changed, 42 insertions, 0 deletions
diff --git a/prolog/problems/lists/len_2/common.py b/prolog/problems/lists/len_2/common.py
index 7dbdc62..6737f33 100644
--- a/prolog/problems/lists/len_2/common.py
+++ b/prolog/problems/lists/len_2/common.py
@@ -1,5 +1,9 @@
 # coding=utf-8
 
+from operator import itemgetter
+import prolog.engine
+import server.problems
+
 id = 119
 number = 26
 visible = True
@@ -11,3 +15,41 @@ len([_|T], Len) :-
   len(T, LenT),
   Len is LenT + 1.
 '''
+
+test_cases = [
+    ('len([8,3,5,1], X)',
+        [{'X': '4'}]),
+    ('len([2,-3,5,0,3], X)',
+        [{'X': '5'}]),
+    ('len([], X)',
+        [{'X': '0'}]),
+]
+
+def test(program, solved_problems):
+    code = (program + '\n' +
+            server.problems.solutions_for_problems('prolog', solved_problems))
+
+    engine_id = None
+    try:
+        engine_id, output = prolog.engine.create(code=code, timeout=1.0)
+        if not engine_id or 'error' in map(itemgetter(0), output):
+            # Engine creation failed, or syntax error in code.
+            return 0, len(test_cases)
+
+        n_correct = 0
+        for query, answers in test_cases:
+            # Limit inferences for each solution to curb unbounded recursion.
+            limited = 'call_with_inference_limit(({}), 100000, _)'.format(query)
+            if prolog.engine.check_answers(engine_id, query=limited, answers=answers, timeout=1.0):
+                n_correct += 1
+    finally:
+        if engine_id:
+            prolog.engine.destroy(engine_id)
+
+    passed = n_correct == len(test_cases)
+    hints = [{'id': 'test_results', 'args': {'passed': n_correct, 'total': len(test_cases)}}]
+    return passed, hints
+
+def hint(program, solved_problems):
+    # TODO
+    return []