test: cover auth-config helpers and oauth2 cache fix

I added 13 new tests across 5 files, covering the auth-config functions that lacked tests. Categories follow Normal / Boundary / Error where applicable.

`cj/toggle-auth-source-debug` flips state once and back through two toggles. `cj/oauth2-auto--plstore-read-fixed` gets three tests: cache miss reads then caches, cache hit skips `plstore-open` entirely, and the `unwind-protect` runs `plstore-close` even when `plstore-get` signals.

`cj/reset-auth-cache` covers no-prefix (skip `shell-command`), with-prefix success, and with-prefix shell failure (Emacs caches still clear). `cj/kill-gpg-agent` covers shell exit 0 and non-zero. `cj/clear-oauth2-auto-cache` covers bound-with-entries, bound-but-empty, and unbound. The unbound test restores the binding via `unwind-protect` so other tests in the same Emacs session don't void-variable.

I stubbed every boundary via `cl-letf` (`plstore-open`, `plstore-get`, `plstore-close`, `oauth2-auto--compute-id`, `auth-source-forget-all-cached`, `epa-file-clear-cache`, `shell-command`, `message`, `call-process`) and didn't stub any internal helpers.

15 auth-config tests pass together: 2 existing plus 13 new.

1 files changed, 42 insertions, 0 deletions

diff --git a/tests/test-auth-config-kill-gpg-agent.el b/tests/test-auth-config-kill-gpg-agent.el
new file mode 100644
index 00000000..8933bee7
--- /dev/null
+++ b/tests/test-auth-config-kill-gpg-agent.el
@@ -0,0 +1,42 @@
+;;; test-auth-config-kill-gpg-agent.el --- Tests for cj/kill-gpg-agent -*- lexical-binding: t; -*-
+
+;;; Commentary:
+;; Verifies cj/kill-gpg-agent reports success or warning based on shell exit code.
+
+;;; Code:
+
+(require 'cl-lib)
+(require 'ert)
+(require 'auth-source)
+
+(add-to-list 'load-path (expand-file-name "modules" user-emacs-directory))
+
+(defun test-auth-config-kill--load ()
+  "Load auth-config with external process calls stubbed."
+  (cl-letf (((symbol-function 'call-process)
+             (lambda (&rest _args) 0)))
+    (load (expand-file-name "modules/auth-config.el" user-emacs-directory)
+          nil t)))
+
+(ert-deftest test-auth-config-kill-gpg-agent-normal-shell-success ()
+  "Normal: shell-command exit 0 yields success message."
+  (test-auth-config-kill--load)
+  (let ((last-message nil))
+    (cl-letf (((symbol-function 'shell-command) (lambda (&rest _) 0))
+              ((symbol-function 'message)
+               (lambda (fmt &rest _) (setq last-message fmt))))
+      (cj/kill-gpg-agent)
+      (should (string-match-p "gpg-agent killed" last-message)))))
+
+(ert-deftest test-auth-config-kill-gpg-agent-error-shell-fails ()
+  "Error: shell-command non-zero yields warning message."
+  (test-auth-config-kill--load)
+  (let ((last-message nil))
+    (cl-letf (((symbol-function 'shell-command) (lambda (&rest _) 1))
+              ((symbol-function 'message)
+               (lambda (fmt &rest _) (setq last-message fmt))))
+      (cj/kill-gpg-agent)
+      (should (string-match-p "Failed to kill gpg-agent" last-message)))))
+
+(provide 'test-auth-config-kill-gpg-agent)
+;;; test-auth-config-kill-gpg-agent.el ends here