test_ctypes.test_find seems to pass when it shouldn't

[rossburton]

Bug report

Bug description:

I have a container that has no compiler but does have ld:

$ gcc --version
-sh: gcc: command not found
$ ld --version
GNU ld (GNU Binutils) 2.46

If I run the test_ctypes tests, specifically test_find_library_with_gcc which looks like it will need gcc, it surprisingly passes:

$ python3 -mtest -v test_ctypes.test_find
== CPython 3.14.5 (main, May 10 2026, 10:21:34) [GCC 16.1.0]
== Linux-6.18.33-yocto-standard-aarch64-with-glibc2.43 little-endian
== Python build: release shared
== cwd: /tmp/test_python_worker_332æ
== CPU count: 4
== encodings: locale=ANSI_X3.4-1968 FS=utf-8
== resources: all test resources are disabled, use -u option to unskip tests

test_find (test.test_ctypes.test_find.FindLibraryAndroid.test_find) ... skipped 'Test only valid for Android'
test_find_nothing_with_wrong_ld_library_path (test.test_ctypes.test_find.FindLibraryEmscripten.test_find_nothing_with_wrong_ld_library_path) ... skipped 'Test only valid for Emscripten'
test_find_nothing_without_ld_library_path (test.test_ctypes.test_find.FindLibraryEmscripten.test_find_nothing_without_ld_library_path) ... skipped 'Test only valid for Emscripten'
test_find_wasm_file_with_so_extension (test.test_ctypes.test_find.FindLibraryEmscripten.test_find_wasm_file_with_so_extension) ... skipped 'Test only valid for Emscripten'
test_find_wasm_file_with_wasm_extension (test.test_ctypes.test_find.FindLibraryEmscripten.test_find_wasm_file_with_wasm_extension) ... skipped 'Test only valid for Emscripten'
test_ignore_non_wasm_file (test.test_ctypes.test_find.FindLibraryEmscripten.test_ignore_non_wasm_file) ... skipped 'Test only valid for Emscripten'
test_find_library_with_gcc (test.test_ctypes.test_find.FindLibraryLinux.test_find_library_with_gcc) ... ok
test_find_library_with_ld (test.test_ctypes.test_find.FindLibraryLinux.test_find_library_with_ld) ... ok
test_find_on_libpath (test.test_ctypes.test_find.FindLibraryLinux.test_find_on_libpath) ... skipped 'gcc, needed for test, not available'
test_gh114257 (test.test_ctypes.test_find.FindLibraryLinux.test_gh114257) ... ok
OpenGL libraries:
	 ('GL', None)
	 ('GLU', None)
	 ('gle', None)
test_gl (test.test_ctypes.test_find.Test_OpenGL_libs.test_gl) ... skipped 'lib_gl not available'
test_gle (test.test_ctypes.test_find.Test_OpenGL_libs.test_gle) ... skipped 'lib_gle not available'
test_glu (test.test_ctypes.test_find.Test_OpenGL_libs.test_glu) ... skipped 'lib_glu not available'
test_shell_injection (test.test_ctypes.test_find.Test_OpenGL_libs.test_shell_injection) ... ok

Specifically:

test_find_library_with_gcc (test.test_ctypes.test_find.FindLibraryLinux.test_find_library_with_gcc) ... ok

CPython versions tested on:

3.14

Operating systems tested on:

Linux

[rossburton]

If I remove ld then the _with_ld test fails (which I expect) but so does the _with_gcc test (which I do not):

FAIL: test_find_library_with_gcc (test.test_ctypes.test_find.FindLibraryLinux.test_find_library_with_gcc)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/usr/lib/python3.14/test/test_ctypes/test_find.py", line 122, in test_find_library_with_gcc
    self.assertNotEqual(find_library('c'), None)
    ~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^
AssertionError: None == None

FAIL: test_find_library_with_ld (test.test_ctypes.test_find.FindLibraryLinux.test_find_library_with_ld)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/usr/lib/python3.14/test/test_ctypes/test_find.py", line 127, in test_find_library_with_ld
    self.assertNotEqual(find_library('c'), None)
    ~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^
AssertionError: None == None

[rossburton]

Ah presumably this is because find_library() does this:

            return _findSoname_ldconfig(name) or \
                   _get_soname(_findLib_gcc(name)) or _get_soname(_findLib_ld(name))

And the _with_gcc test mocks _findSoname_ldconfig but not _findLib_ld.

[rossburton]

I have some patches, will finish and post.