quick random testing module for python and some random tests for bson

bson.py

@@ -8,7 +8,7 @@ import struct
 import random
 import re
 
-from test import test_data
+from test import test_data, qcheck
 
 class InvalidBSON(ValueError):
     """Raised when trying to create a BSON object from invalid data.
@@ -328,17 +328,7 @@ class TestBSON(unittest.TestCase):
             self.assertTrue(is_valid(data))
 
     def test_random_data_is_not_bson(self):
-        def random_char(size):
-            return chr(random.randint(0, 255))
-
-        def random_string(size):
-            return "".join(random_list(random_char)(size))
-
-        def random_list(generator):
-            return lambda size: [generator(size) for _ in range(size)]
-
-        for i in range(100):
-            self.assertFalse(is_valid(random_string(i)))
+        qcheck.check_unittest(self, qcheck.isnt(is_valid), qcheck.gen_string(qcheck.gen_range(0, 40)))
 
     def test_basic_from_dict(self):
         self.assertRaises(TypeError, BSON.from_dict, 100)

test/qcheck.py

@@ -0,0 +1,39 @@
+import random
+
+gen_target = 100
+examples = 5
+
+def gen_range(start, stop):
+    return lambda: random.randint(start, stop)
+
+def char():
+    return chr(random.randint(0, 255))
+
+def gen_string(gen_length):
+    return lambda: "".join(gen_list(char, gen_length))
+
+def gen_list(generator, length):
+    return [generator() for _ in range(length())]
+
+
+def isnt(predicate):
+    return lambda x: not predicate(x)
+
+
+def check(predicate, generator):
+    counter_examples = []
+    for i in range(gen_target):
+        case = generator()
+        if not predicate(case):
+            counter_examples.append(repr(case))
+    return counter_examples
+
+def check_unittest(test, predicate, generator):
+    counter_examples = check(predicate, generator)
+    if counter_examples:
+        failures = len(counter_examples)
+        message = "\n".join(["    -> %s" % f for f in counter_examples[:examples]])
+        message = "found %d counter examples, displaying first %d:\n%s" % (failures,
+                                                                          min(failures, examples),
+                                                                          message)
+        test.fail(message)