Add parameter checks for stringify_set

vladiate/test/test_validators.py

@@ -224,6 +224,14 @@ def test_all_validators_support_empty_ok(validator_class, args):
     ({'A', 'B', 'C'}, 2, "{'A', 'B'} (1 more suppressed)"),
     ({'A', 'B', 'C'}, 0, "{} (3 more suppressed)"),
     ({}, 5, "{}"),
+    ({}, 0, "{}"),
 ])
 def test_stringify_set(a_set, max_len, stringified):
     assert stringify_set(a_set, max_len) == stringified
+
+
+def test_stringify_set_invalid_params():
+    with pytest.raises(ValueError):
+        stringify_set({}, -1, 10)
+    with pytest.raises(ValueError):
+        stringify_set({}, 10, -1)

vladiate/validators.py

@@ -219,6 +219,11 @@ def stringify_set(a_set, max_len, max_sort_size=8192):
     Large sets won't be sorted for performance reasons.
     This may result in an arbitrary ordering in the returned string.
     '''
+    if max_len < 0:
+        raise ValueError("max_len must be non-negative: {}".format(max_len))
+    if max_sort_size < 0:
+        raise ValueError(
+            "max_sort_size must be non-negative: {}".format(max_sort_size))
     # Don't convert `a_set` to a list for performance reasons
     text = "{{{}}}".format(", ".join(
         "'{}'".format(value) for value in islice(