gh-151814: Add test for TextIOWrapper.write unbounded memory growth from repeated writes (GH-152244)

Use tracemalloc to measure memory usage.

Author: cmaloney

Lib/test/test_io/test_textio.py

@@ -6,6 +6,7 @@
 import sys
 import threading
 import time
+import tracemalloc
 import unittest
 import warnings
 import weakref
@@ -1580,6 +1581,21 @@ def write(self, data):
         t.write("x"*chunk_size)
         self.assertEqual([b"abcdef", b"ghi", b"x"*chunk_size], buf._write_stack)
 
+    def test_write_empty_no_memory_growth(self):
+        # gh-151814: Writing empty string should have stable memory usage.
+        t = self.TextIOWrapper(self.BytesIO())
+        nwrites = 200_000
+        tracemalloc.start()
+        try:
+            for _ in range(nwrites):
+                t.write("")
+            _, peak = tracemalloc.get_traced_memory()
+        finally:
+            tracemalloc.stop()
+
+        # No longer leaks several bytes per write.
+        self.assertLess(peak, nwrites)
+
     def test_issue119506(self):
         chunk_size = 8192