Test peek() after write()

Author: marcelm

Lib/test/test_io/test_memoryio.py

@@ -589,6 +589,16 @@ def test_peek(self):
             self.assertEqual(memio.tell(), len(buf))
             self.assertEqual(memio.peek(1), self.EOF)
             self.assertEqual(memio.tell(), len(buf))
+            # Peeking works after writing
+            abc = self.buftype("abc")
+            memio.write(abc)
+            self.assertEqual(memio.peek(), self.EOF)
+            memio.seek(len(buf))
+            self.assertEqual(memio.peek(), abc[:1])
+            self.assertEqual(memio.peek(-1), abc)
+            self.assertEqual(memio.peek(len(abc) + 100), abc)
+            self.assertEqual(memio.tell(), len(buf))
+
         self.assertRaises(ValueError, memio.peek)
 
     def test_unicode(self):