push preserved contexts in correct order (#5797)

CHANGES.rst

@@ -3,6 +3,9 @@ Version 3.1.2
 
 Unreleased
 
+-   When using ``follow_redirects`` in the test client, the final state
+    of ``session`` is correct. :issue:`5786`
+
 
 Version 3.1.1
 -------------

src/flask/testing.py

@@ -240,10 +240,10 @@ class FlaskClient(Client):
         response.json_module = self.application.json  # type: ignore[assignment]
 
         # Re-push contexts that were preserved during the request.
-        while self._new_contexts:
-            cm = self._new_contexts.pop()
+        for cm in self._new_contexts:
             self._context_stack.enter_context(cm)
 
+        self._new_contexts.clear()
         return response
 
     def __enter__(self) -> FlaskClient:

tests/test_testing.py

@@ -138,32 +138,21 @@ def test_blueprint_with_subdomain():
     assert rv.data == b"http://xxx.example.com:1234/foo/"
 
 
-def test_redirect_keep_session(app, client, app_ctx):
-    @app.route("/", methods=["GET", "POST"])
+def test_redirect_session(app, client, app_ctx):
+    @app.route("/redirect")
     def index():
-        if flask.request.method == "POST":
-            return flask.redirect("/getsession")
-        flask.session["data"] = "foo"
-        return "index"
+        flask.session["redirect"] = True
+        return flask.redirect("/target")
 
-    @app.route("/getsession")
+    @app.route("/target")
     def get_session():
-        return flask.session.get("data", "<missing>")
+        flask.session["target"] = True
+        return ""
 
     with client:
-        rv = client.get("/getsession")
-        assert rv.data == b"<missing>"
-
-        rv = client.get("/")
-        assert rv.data == b"index"
-        assert flask.session.get("data") == "foo"
-
-        rv = client.post("/", data={}, follow_redirects=True)
-        assert rv.data == b"foo"
-        assert flask.session.get("data") == "foo"
-
-        rv = client.get("/getsession")
-        assert rv.data == b"foo"
+        client.get("/redirect", follow_redirects=True)
+        assert flask.session["redirect"] is True
+        assert flask.session["target"] is True
 
 
 def test_session_transactions(app, client):