Support non-sliceable containers in uniqueness assertions

docs/changelog.rst

@@ -3,6 +3,8 @@ Changelog
 =========
 
 * :release:`0.12.3 <2023-12-20>`
+* :bug:`74` Support uniqueness assertions for iterable containers that do not
+  support slicing
 * :bug:`128` Properly handle assertion failures during setUp/tearDown
 * :support:`145` Support Python 3.12 (and drop 3.8)
 * :release:`0.12.2 <2023-12-20>`

marbles/mixins/marbles/mixins/mixins.py

@@ -359,6 +359,15 @@ class UniqueMixins(abc.ABC):
     elements.
     '''
 
+    @staticmethod
+    def _unique(container):
+        seen = []
+        for elem in container:
+            if elem in seen:
+                return False
+            seen.append(elem)
+        return True
+
     @abc.abstractmethod
     def fail(self, msg):
         pass  # pragma: no cover
@@ -391,14 +400,8 @@ def assertUnique(self, container, msg=None):
 
         standardMsg = 'Elements in %s are not unique' % (container,)
 
-        # We iterate over each element in the container instead of
-        # comparing len(container) == len(set(container)) to allow
-        # for containers that contain unhashable types
-        for idx, elem in enumerate(container):
-            # If elem appears at an earlier or later index position
-            # the elements are not unique
-            if elem in container[:idx] or elem in container[idx+1:]:
-                self.fail(self._formatMessage(msg, standardMsg))
+        if not self._unique(container):
+            self.fail(self._formatMessage(msg, standardMsg))
 
     def assertNotUnique(self, container, msg=None):
         '''Fail if elements in ``container`` are unique.
@@ -420,16 +423,8 @@ def assertNotUnique(self, container, msg=None):
 
         standardMsg = 'Elements in %s are unique' % (container,)
 
-        # We iterate over each element in the container instead of
-        # comparing len(container) == len(set(container)) to allow
-        # for containers that contain unhashable types
-        for idx, elem in enumerate(container):
-            # If elem appears at an earlier or later index position
-            # the elements are not unique
-            if elem in container[:idx] or elem in container[idx+1:]:
-                return  # succeed fast
-
-        self.fail(self._formatMessage(msg, standardMsg))
+        if self._unique(container):
+            self.fail(self._formatMessage(msg, standardMsg))
 
 
 class FileMixins(abc.ABC):

marbles/mixins/tests/test_mixins.py

@@ -23,6 +23,7 @@
 import operator
 import os
 import unittest
+from collections import deque
 from unittest import mock
 from datetime import date, datetime, timedelta, timezone
 
@@ -268,6 +269,21 @@ def test_assert_unique(self):
             self.kls.assertNotUnique([set([1, 2, 3]), set([2, 3, 4])])
         self.assertEqual(e.exception.args[0], msg)
 
+        # containers that are iterable but do not support slicing
+        self.kls.assertUnique(deque([1, 2, 3]))
+
+        msg = 'Elements in %s are not unique' % (deque([1, 2, 1]),)
+        with self.assertRaises(AssertionError) as e:
+            self.kls.assertUnique(deque([1, 2, 1]))
+        self.assertEqual(e.exception.args[0], msg)
+
+        self.kls.assertNotUnique(deque([1, 2, 1]))
+
+        msg = 'Elements in %s are unique' % (deque([1, 2, 3]),)
+        with self.assertRaises(AssertionError) as e:
+            self.kls.assertNotUnique(deque([1, 2, 3]))
+        self.assertEqual(e.exception.args[0], msg)
+
 
 class TestFileMixins(unittest.TestCase):