From a4242a95a18a3beeebc2cb370fe0cc129702ffe7 Mon Sep 17 00:00:00 2001
From: Jelle Zijlstra <jelle.zijlstra@gmail.com>
Date: Tue, 25 Jan 2022 12:42:19 -0800
Subject: [PATCH] fix assert_stable

---
 src/black/__init__.py | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/src/black/__init__.py b/src/black/__init__.py
index 1f501ef45f..769e693ed2 100644
--- a/src/black/__init__.py
+++ b/src/black/__init__.py
@@ -1367,7 +1367,10 @@ def assert_equivalent(src: str, dst: str, *, pass_num: int = 1) -> None:
 
 def assert_stable(src: str, dst: str, mode: Mode) -> None:
     """Raise AssertionError if `dst` reformats differently the second time."""
-    newdst = format_str(dst, mode=mode)
+    # We shouldn't call format_str() here, because that formats the string
+    # twice and may hide a bug where we bounce back and forth between two
+    # versions.
+    newdst = _format_str_once(dst, mode=mode)
     if dst != newdst:
         log = dump_to_file(
             str(mode),