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, 86 insertions, 0 deletions

diff --git a/tests/test-auth-config-oauth2-auto-plstore-read-fixed.el b/tests/test-auth-config-oauth2-auto-plstore-read-fixed.el
new file mode 100644
index 000000000..25446dec5
--- /dev/null
+++ b/tests/test-auth-config-oauth2-auto-plstore-read-fixed.el
@@ -0,0 +1,86 @@
+;;; test-auth-config-oauth2-auto-plstore-read-fixed.el --- Tests for oauth2 cache fix -*- lexical-binding: t; -*-
+
+;;; Commentary:
+;; Confirms the oauth2-auto plstore-read advice caches reads on miss,
+;; skips plstore-open on hit, and runs plstore-close even when
+;; plstore-get signals.
+
+;;; Code:
+
+(require 'cl-lib)
+(require 'ert)
+(require 'auth-source)
+
+(add-to-list 'load-path (expand-file-name "modules" user-emacs-directory))
+
+(defvar oauth2-auto--plstore-cache nil
+  "Stub for oauth2-auto's in-memory token cache.")
+
+(defvar oauth2-auto-plstore "/tmp/test-oauth2-stub.plist"
+  "Stub for oauth2-auto plstore path.")
+
+(defun test-auth-config-oauth2--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))
+  (setq oauth2-auto--plstore-cache (make-hash-table :test 'equal)))
+
+(ert-deftest test-auth-config-oauth2-plstore-read-normal-cache-miss-reads-and-caches ()
+  "Normal: cache miss opens plstore, reads value, caches, returns value."
+  (test-auth-config-oauth2--load)
+  (let ((opens 0)
+        (closes 0))
+    (cl-letf (((symbol-function 'require) (lambda (&rest _) t))
+              ((symbol-function 'oauth2-auto--compute-id)
+               (lambda (_u _p) "stable-id"))
+              ((symbol-function 'plstore-open)
+               (lambda (_) (cl-incf opens) 'fake-plstore))
+              ((symbol-function 'plstore-get)
+               (lambda (_p id) (cons id "secret-value")))
+              ((symbol-function 'plstore-close)
+               (lambda (_) (cl-incf closes))))
+      (let ((result (cj/oauth2-auto--plstore-read-fixed "u" "p")))
+        (should (equal result "secret-value"))
+        (should (= opens 1))
+        (should (= closes 1))
+        (should (equal (gethash "stable-id" oauth2-auto--plstore-cache)
+                       "secret-value"))))))
+
+(ert-deftest test-auth-config-oauth2-plstore-read-boundary-cache-hit-skips-plstore ()
+  "Boundary: cache hit returns cached value without opening plstore."
+  (test-auth-config-oauth2--load)
+  (puthash "stable-id" "cached-value" oauth2-auto--plstore-cache)
+  (let ((opens 0))
+    (cl-letf (((symbol-function 'require) (lambda (&rest _) t))
+              ((symbol-function 'oauth2-auto--compute-id)
+               (lambda (_u _p) "stable-id"))
+              ((symbol-function 'plstore-open)
+               (lambda (_) (cl-incf opens) 'fake-plstore))
+              ((symbol-function 'plstore-get)
+               (lambda (_p _id) (error "plstore-get should not be called")))
+              ((symbol-function 'plstore-close)
+               (lambda (_) nil)))
+      (let ((result (cj/oauth2-auto--plstore-read-fixed "u" "p")))
+        (should (equal result "cached-value"))
+        (should (zerop opens))))))
+
+(ert-deftest test-auth-config-oauth2-plstore-read-error-plstore-close-runs-after-get-fails ()
+  "Error: plstore-close runs even when plstore-get signals an error."
+  (test-auth-config-oauth2--load)
+  (let ((closes 0))
+    (cl-letf (((symbol-function 'require) (lambda (&rest _) t))
+              ((symbol-function 'oauth2-auto--compute-id)
+               (lambda (_u _p) "stable-id"))
+              ((symbol-function 'plstore-open)
+               (lambda (_) 'fake-plstore))
+              ((symbol-function 'plstore-get)
+               (lambda (_p _id) (error "boom")))
+              ((symbol-function 'plstore-close)
+               (lambda (_) (cl-incf closes))))
+      (should-error (cj/oauth2-auto--plstore-read-fixed "u" "p"))
+      (should (= closes 1)))))
+
+(provide 'test-auth-config-oauth2-auto-plstore-read-fixed)
+;;; test-auth-config-oauth2-auto-plstore-read-fixed.el ends here