1 files changed, 36 insertions, 1 deletions
diff --git a/Lib/test/test_pyrepl/test_utils.py b/Lib/test/test_pyrepl/test_utils.py
index 0d59968206a..8ce1e537138 100644
--- a/Lib/test/test_pyrepl/test_utils.py
+++ b/Lib/test/test_pyrepl/test_utils.py
@@ -1,6 +1,6 @@
 from unittest import TestCase
 
-from _pyrepl.utils import str_width, wlen
+from _pyrepl.utils import str_width, wlen, prev_next_window
 
 
 class TestUtils(TestCase):
@@ -25,3 +25,38 @@ class TestUtils(TestCase):
 
         self.assertEqual(wlen('hello'), 5)
         self.assertEqual(wlen('hello' + '\x1a'), 7)
+
+    def test_prev_next_window(self):
+        def gen_normal():
+            yield 1
+            yield 2
+            yield 3
+            yield 4
+
+        pnw = prev_next_window(gen_normal())
+        self.assertEqual(next(pnw), (None, 1, 2))
+        self.assertEqual(next(pnw), (1, 2, 3))
+        self.assertEqual(next(pnw), (2, 3, 4))
+        self.assertEqual(next(pnw), (3, 4, None))
+        with self.assertRaises(StopIteration):
+            next(pnw)
+
+        def gen_short():
+            yield 1
+
+        pnw = prev_next_window(gen_short())
+        self.assertEqual(next(pnw), (None, 1, None))
+        with self.assertRaises(StopIteration):
+            next(pnw)
+
+        def gen_raise():
+            yield from gen_normal()
+            1/0
+
+        pnw = prev_next_window(gen_raise())
+        self.assertEqual(next(pnw), (None, 1, 2))
+        self.assertEqual(next(pnw), (1, 2, 3))
+        self.assertEqual(next(pnw), (2, 3, 4))
+        self.assertEqual(next(pnw), (3, 4, None))
+        with self.assertRaises(ZeroDivisionError):
+            next(pnw)