From 94fd8fc5dc9560c6f78e9b832cfd2d5724197192 Mon Sep 17 00:00:00 2001
From: Jammy2211 <JNightingale2211@gmail.com>
Date: Wed, 7 Oct 2026 08:40:07 +0100
Subject: [PATCH] test: cover fork_context() darwin/win32 branch (no
 start-method fix at import)

Monkeypatch sys.platform to darwin/win32 and assert fork_context()
returns the multiprocessing module (Process/Queue/Pool) and never calls
multiprocessing.get_context() with no argument, the import-time call
that fixed the default start method before #1657.

Closes #1661

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
---
 test_autofit/non_linear/test_fork_context.py | 50 ++++++++++++++++++++
 1 file changed, 50 insertions(+)

diff --git a/test_autofit/non_linear/test_fork_context.py b/test_autofit/non_linear/test_fork_context.py
index 5857cb205..d5acf06e9 100644
--- a/test_autofit/non_linear/test_fork_context.py
+++ b/test_autofit/non_linear/test_fork_context.py
@@ -43,6 +43,56 @@ def test_fork_context_valid_everywhere():
     assert fork_context().get_start_method() in multiprocessing.get_all_start_methods()
 
 
+@pytest.mark.parametrize("platform", ["darwin", "win32"])
+def test_fork_context_non_fork_platform_returns_module(monkeypatch, platform):
+    """
+    On macOS (and on platforms without "fork") ``fork_context()`` returns the
+    ``multiprocessing`` module itself, which exposes the same Process / Queue /
+    Pool API and defers the start-method choice until a process starts.
+    """
+    monkeypatch.setattr(sys, "platform", platform)
+    if platform == "win32":
+        monkeypatch.setattr(multiprocessing, "get_all_start_methods", lambda: ["spawn"])
+
+    context = fork_context()
+
+    assert context is multiprocessing
+    for name in ("Process", "Queue", "Pool"):
+        assert hasattr(context, name)
+
+
+@pytest.mark.parametrize("platform", ["darwin", "win32"])
+def test_fork_context_non_fork_platform_does_not_fix_start_method(
+    monkeypatch, platform
+):
+    """
+    Regression test for PyAutoFit#1657: ``fork_context()`` runs at import time
+    (``class Process(fork_context().Process)``), and the no-argument
+    ``multiprocessing.get_context()`` call it used to make on macOS/Windows
+    fixed the interpreter's default start method, so a later
+    ``multiprocessing.set_start_method(...)`` raised "context has already been
+    set". The non-fork branch must never call ``get_context()`` without a
+    method.
+    """
+    monkeypatch.setattr(sys, "platform", platform)
+    if platform == "win32":
+        monkeypatch.setattr(multiprocessing, "get_all_start_methods", lambda: ["spawn"])
+
+    calls = []
+    real_get_context = multiprocessing.get_context
+
+    def spy_get_context(*args, **kwargs):
+        calls.append((args, kwargs))
+        return real_get_context(*args, **kwargs)
+
+    monkeypatch.setattr(multiprocessing, "get_context", spy_get_context)
+
+    fork_context()
+
+    assert ((), {}) not in calls
+    assert ((None,), {}) not in calls
+
+
 @requires_fork
 def test_process_class_is_fork_bound():
     assert Process._start_method == "fork"