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+;;; test-org-drill-first-function.el --- Test org-drill 'first' function compatibility -*- lexical-binding: t -*-
+
+;;; Commentary:
+;;
+;; Tests to reproduce and verify the fix for org-drill's use of deprecated
+;; 'first' function which was removed in modern Emacs.
+;;
+;; Original error: "mapcar: Symbol's function definition is void: first"
+;;
+;; The error occurred because org-drill (or its dependencies) use old Common Lisp
+;; functions like 'first' instead of the modern 'cl-first' from cl-lib.
+
+;;; Code:
+
+(require 'ert)
+
+(ert-deftest test-org-drill-first-function-not-defined-without-compat ()
+  "Verify that 'first' function doesn't exist by default in modern Emacs.
+
+This test documents the original problem - the 'first' function from the
+old 'cl' package is not available in modern Emacs, which only provides
+'cl-first' from cl-lib."
+  (let ((first-defined (fboundp 'first)))
+    ;; In a clean Emacs without our compatibility shim, 'first' should not exist
+    ;; (unless the old 'cl' package was loaded, which is deprecated)
+    (should (or (not first-defined)
+                ;; If it IS defined, it should be our compatibility alias
+                (eq (symbol-function 'first) 'cl-first)))))
+
+(ert-deftest test-org-drill-cl-first-is-available ()
+  "Verify that cl-first is available from cl-lib.
+
+The modern cl-lib package provides cl-first as the replacement for
+the deprecated 'first' function."
+  (require 'cl-lib)
+  (should (fboundp 'cl-first))
+  ;; Test it works
+  (should (eq 'a (cl-first '(a b c)))))
+
+(ert-deftest test-org-drill-first-compatibility-alias ()
+  "Verify that our compatibility alias makes 'first' work like 'cl-first'.
+
+This is the fix we applied - creating an alias so that code using the
+old 'first' function will work with the modern 'cl-first'."
+  (require 'cl-lib)
+
+  ;; Create the compatibility alias (same as in org-drill-config.el)
+  (unless (fboundp 'first)
+    (defalias 'first 'cl-first))
+
+  ;; Now 'first' should be defined
+  (should (fboundp 'first))
+
+  ;; And it should behave like cl-first
+  (should (eq 'a (first '(a b c))))
+  (should (eq 'x (first '(x y z))))
+  (should (eq nil (first '()))))
+
+(ert-deftest test-org-drill-mapcar-with-first ()
+  "Test the exact error scenario: (mapcar 'first ...).
+
+This reproduces the original error that occurred during org-drill's
+item collection phase where it uses mapcar with the 'first' function."
+  (require 'cl-lib)
+
+  ;; Create the compatibility alias
+  (unless (fboundp 'first)
+    (defalias 'first 'cl-first))
+
+  ;; Simulate org-drill data structure: list of (status data) pairs
+  (let ((drill-entries '((:new 0 0)
+                         (:young 5 3)
+                         (:overdue 10 2)
+                         (:mature 20 1))))
+
+    ;; This is the kind of operation that was failing
+    ;; Extract first element from each entry
+    (let ((statuses (mapcar 'first drill-entries)))
+      (should (equal statuses '(:new :young :overdue :mature))))))
+
+(ert-deftest test-org-drill-second-and-third-aliases ()
+  "Verify that second and third compatibility aliases also work.
+
+org-drill might use other deprecated cl functions too, so we create
+aliases for second and third as well."
+  (require 'cl-lib)
+
+  ;; Create all compatibility aliases
+  (unless (fboundp 'first)
+    (defalias 'first 'cl-first))
+  (unless (fboundp 'second)
+    (defalias 'second 'cl-second))
+  (unless (fboundp 'third)
+    (defalias 'third 'cl-third))
+
+  (let ((test-list '(a b c d e)))
+    (should (eq 'a (first test-list)))
+    (should (eq 'b (second test-list)))
+    (should (eq 'c (third test-list)))))
+
+(ert-deftest test-org-drill-config-loads-without-error ()
+  "Verify that org-drill-config.el loads successfully with our fix.
+
+This test ensures that the :init block in our use-package form
+doesn't cause any loading errors."
+  ;; This should not throw an error
+  (should-not (condition-case err
+                  (progn
+                    (load (expand-file-name "modules/org-drill-config.el"
+                                            user-emacs-directory))
+                    nil)
+                (error err))))
+
+(ert-deftest test-org-drill-data-structure-operations ()
+  "Verify that common org-drill data structure operations work with our fix.
+
+org-drill works with data structures that require extracting elements.
+This test ensures our compatibility aliases work with typical patterns."
+  (require 'cl-lib)
+
+  ;; Create compatibility aliases
+  (unless (fboundp 'first)
+    (defalias 'first 'cl-first))
+
+  ;; Test that we can work with org-drill-like data structures
+  ;; (similar to what persist-defvar would store)
+  (let ((test-data '((:status-1 data-1)
+                     (:status-2 data-2)
+                     (:status-3 data-3))))
+    ;; This kind of operation should work
+    (should (equal '(:status-1 :status-2 :status-3)
+                   (mapcar 'first test-data)))))
+
+(provide 'test-org-drill-first-function)
+;;; test-org-drill-first-function.el ends here