chore: coverage, autoload fix, and internal cleanup for org-drill

A batch of test-coverage and hardening work, squashed from the test-work branch.

Tests: deduplicated a colliding leitner-capture test name so make test-name loads again. Added SM2 assert-failure cases, the six basic multicloze variant delegations, the three English-side spanish-verb branches, and org-drill-current-scope branch coverage.

Fix: the entry-point commands (org-drill itself, cram-tree, tree, directory, resume, relearn-item, strip-all-data, merge-buffers) carried no autoload cookies, so M-x failed from a fresh install until something pulled the file in. They're autoloaded now.

Perf: org-drill-shuffle was quadratic because it indexed a list with elt on every swap. It runs a linear Fisher-Yates pass over a vector now, and it checks its argument is a list.

Feat: added org-drill-version, a constant plus an interactive command, so a bug reporter doesn't have to open the file header.

Refactor: extracted org-drill--format-tense-mood, shared by the two verb-conjugation presenters that each carried a copy.

Docs: explained the SM8 magic numbers in the simple8 helpers as empirical fits rather than tunable knobs.

11 files changed, 345 insertions, 41 deletions

diff --git a/org-drill.el b/org-drill.el
index d52fbe9..836f754 100644
--- a/org-drill.el
+++ b/org-drill.el
@@ -64,6 +64,18 @@
   :tag "Org-Drill"
   :group 'org-link)
 
+(defconst org-drill-version "2.7.0"
+  "Version of the org-drill package.
+Keep this in sync with the Version header at the top of this file.")
+
+;;;###autoload
+(defun org-drill-version ()
+  "Report the installed org-drill version in the echo area.
+Returns the version string so it is useful in non-interactive code too."
+  (interactive)
+  (message "org-drill %s" org-drill-version)
+  org-drill-version)
+
 (defcustom org-drill-question-tag
   "drill"
   "Tag for topics which are review topics."
@@ -1271,6 +1283,10 @@ Returns a list:
 
 Returns the optimal FIRST interval for an item which has previously been
 forgotten on FAILURES occasions."
+  ;; SM8 first-interval model.  An item never forgotten gets ~2.4849 days;
+  ;; each prior failure shrinks that by a factor of e^-0.057 (~5.5% per
+  ;; failure).  Both constants are the empirical fit from the SM8 algorithm
+  ;; and are not meant to be tuned individually.
   (* 2.4849 (exp (* -0.057 failures))))
 
 (defun org-drill-simple8-interval-factor (ease repetition)
@@ -1281,11 +1297,19 @@ forgotten on FAILURES occasions."
 Returns:
 The factor by which the last interval should be
 multiplied to give the next interval. Corresponds to `RF' or `OF'."
+  ;; 1.2 is the SM8 floor for the interval factor: it never drops below 1.2,
+  ;; so intervals always grow.  The amount above the floor decays as
+  ;; learn-fraction raised to log2(repetition), pulling later repetitions
+  ;; toward the floor.
   (+ 1.2 (* (- ease 1.2) (expt org-drill-learn-fraction (log repetition 2)))))
 
 (defun org-drill-simple8-quality->ease (quality)
   "Returns the ease (`AF' in the SM8 algorithm) which corresponds
 to a mean item quality of QUALITY."
+  ;; Quality (0-5 mean recall score) maps to ease/AF through this 4th-degree
+  ;; polynomial, a least-squares fit carried over from the SM8 algorithm.
+  ;; The five coefficients are empirical and only meaningful together, so
+  ;; treat them as one fitted curve rather than independent knobs.
   (+ (* 0.0542 (expt quality 4))
      (* -0.4848 (expt quality 3))
      (* 1.4916 (expt quality 2))
@@ -3142,6 +3166,7 @@ and optionally saves buffers."
     (sit-for 1)
     (message nil))))
 
+;;;###autoload
 (defun org-drill (&optional scope drill-match resume-p cram)
   "Begin an interactive \\='drill session\\='. The user is asked to
 review a series of topics (headers). Each topic is initially
@@ -3223,6 +3248,7 @@ hours."
   (interactive)
   (org-drill scope drill-match nil t))
 
+;;;###autoload
 (defun org-drill-cram-tree ()
   "Run  an interactive drill session in \\='cram mode\\=' using subtree at point.
 
@@ -3230,12 +3256,14 @@ See also, `org-drill-cram' and `org-drill-tree'."
   (interactive)
   (org-drill-cram 'tree))
 
+;;;###autoload
 (defun org-drill-tree ()
   "Run an interactive drill session using drill items within the
 subtree at point."
   (interactive)
   (org-drill 'tree))
 
+;;;###autoload
 (defun org-drill-directory ()
   "Run an interactive drill session using drill items from all org
 files in the same directory as the current file."
@@ -3265,6 +3293,7 @@ scan will be performed."
      (t
       (org-drill scope drill-match)))))
 
+;;;###autoload
 (defun org-drill-resume ()
   "Resume a suspended drill session. Sessions are suspended by
 exiting them with the `edit' or `quit' options."
@@ -3287,6 +3316,7 @@ need reviewing.  Start a new drill session? "
       (message "You have finished the drill session.")))))
 
 
+;;;###autoload
 (defun org-drill-relearn-item ()
   "Make the current item due for revision, and set its last interval to 0.
 Makes the item behave as if it has been failed, without actually recording a
@@ -3301,6 +3331,7 @@ failure. This command can be used to \\='reset\\=' repetitions for an item."
   (org-schedule '(4)))
 
 
+;;;###autoload
 (defun org-drill-strip-all-data (&optional scope)
   "Delete scheduling data from every drill entry in scope. This
 function may be useful if you want to give your collection of
@@ -3450,6 +3481,7 @@ deck owner is opting in to a clean migration."
              (set-marker m nil))
            org-drill-dest-id-table))
 
+;;;###autoload
 (defun org-drill-merge-buffers (src &optional dest ignore-new-items-p)
   "SRC and DEST are two org mode buffers containing drill items.
 For each drill item in DEST that shares an ID with an item in SRC,
@@ -3543,32 +3575,34 @@ the name of the tense.")
     (if mood (setq mood (propertize mood 'face highlight-face)))
     (list infinitive inf-hint translation tense mood)))
 
+(defun org-drill--format-tense-mood (tense mood)
+  "Return a human-readable label for a verb's TENSE and MOOD.
+Either argument may be nil.  Returns nil when both are nil."
+  (cond
+   ((and tense mood)
+    (format "%s tense, %s mood" tense mood))
+   (tense
+    (format "%s tense" tense))
+   (mood
+    (format "%s mood" mood))))
+
 (defun org-drill-present-verb-conjugation (session)
   "Present a drill entry whose card type is \\='conjugate\\='."
-  (cl-flet ((tense-and-mood-to-string
-             (tense mood)
-             (cond
-              ((and tense mood)
-               (format "%s tense, %s mood" tense mood))
-              (tense
-               (format "%s tense" tense))
-              (mood
-               (format "%s mood" mood)))))
-    (cl-destructuring-bind (infinitive inf-hint translation tense mood)
-        (org-drill-get-verb-conjugation-info)
-      (org-drill-present-card-using-text
-       session
-       (cond
-        ((zerop (cl-random 2))
-         (format "\nTranslate the verb\n\n%s\n\nand conjugate for the %s.\n\n"
-                 infinitive (tense-and-mood-to-string tense mood)))
-
-        (t
-         (format "\nGive the verb that means\n\n%s %s\n
+  (cl-destructuring-bind (infinitive inf-hint translation tense mood)
+      (org-drill-get-verb-conjugation-info)
+    (org-drill-present-card-using-text
+     session
+     (cond
+      ((zerop (cl-random 2))
+       (format "\nTranslate the verb\n\n%s\n\nand conjugate for the %s.\n\n"
+               infinitive (org-drill--format-tense-mood tense mood)))
+
+      (t
+       (format "\nGive the verb that means\n\n%s %s\n
 and conjugate for the %s.\n\n"
-                 translation
-                 (if inf-hint (format "  [HINT: %s]" inf-hint) "")
-                 (tense-and-mood-to-string tense mood))))))))
+               translation
+               (if inf-hint (format "  [HINT: %s]" inf-hint) "")
+               (org-drill--format-tense-mood tense mood)))))))
 
 (defun org-drill-show-answer-verb-conjugation (session reschedule-fn)
  "Show the answer for a drill item whose card type is \\='conjugate\\='.
@@ -3578,14 +3612,7 @@ returns its return value."
       (org-drill-get-verb-conjugation-info)
     (org-drill-with-replaced-entry-heading
      (format "%s of %s ==> %s\n\n"
-             (capitalize
-              (cond
-               ((and tense mood)
-                (format "%s tense, %s mood" tense mood))
-               (tense
-                (format "%s tense" tense))
-               (mood
-                (format "%s mood" mood))))
+             (capitalize (org-drill--format-tense-mood tense mood))
              infinitive translation)
      (org-drill-hide-drawers)
      (funcall reschedule-fn session))))
@@ -3852,12 +3879,16 @@ Returns a list of strings."
     (setf (elt LIST el2) tmp)))
 
 (defun org-drill-shuffle (LIST)
-  "Shuffle the elements in LIST.
-shuffling is done in place."
-  (cl-loop for i in (reverse (number-sequence 1 (1- (length LIST))))
-        do (let ((j (random (+ i 1))))
-             (org-drill-swap LIST i j)))
-  LIST)
+  "Return a random permutation of the elements in LIST.
+The shuffle runs over a temporary vector with a Fisher-Yates pass,
+so the cost is linear in the length of LIST rather than quadratic
+\(the previous version indexed a list with `elt' on every swap)."
+  (cl-check-type LIST list)
+  (let ((vec (vconcat LIST)))
+    (cl-loop for i from (1- (length vec)) downto 1
+             do (let ((j (random (1+ i))))
+                  (cl-rotatef (aref vec i) (aref vec j))))
+    (append vec nil)))
 
 (defun org-drill-leitner-start-box (number)
   "Box some items for the first time."
diff --git a/tests/test-org-drill-autoloads.el b/tests/test-org-drill-autoloads.el
new file mode 100644
index 0000000..5bfefce
--- /dev/null
+++ b/tests/test-org-drill-autoloads.el
@@ -0,0 +1,47 @@
+;;; test-org-drill-autoloads.el --- Autoload-cookie coverage  -*- lexical-binding: t; -*-
+
+;;; Commentary:
+;; The user-facing entry-point commands must carry an `;;;###autoload' cookie
+;; so they work from a fresh package install before org-drill is loaded.
+;; Without it, `M-x org-drill-resume' (etc.) fails with "command not found"
+;; until something pulls the file in.
+;;
+;; This reads the source via `find-library-name' (the .el, not a compiled
+;; .elc which would have the cookies stripped) and checks each command.
+
+;;; Code:
+
+(require 'ert)
+(require 'org-drill)
+
+(defconst test-org-drill-autoloaded-commands
+  '("org-drill"
+    "org-drill-cram"
+    "org-drill-cram-tree"
+    "org-drill-tree"
+    "org-drill-directory"
+    "org-drill-again"
+    "org-drill-resume"
+    "org-drill-relearn-item"
+    "org-drill-strip-all-data"
+    "org-drill-merge-buffers")
+  "Entry-point commands that should be autoloaded.")
+
+(ert-deftest test-org-drill-entry-commands-carry-autoload-cookie ()
+  "Each user-facing entry-point command is preceded by an autoload cookie."
+  (let ((src (with-temp-buffer
+               (insert-file-contents (find-library-name "org-drill"))
+               (buffer-string))))
+    (dolist (cmd test-org-drill-autoloaded-commands)
+      (should (string-match-p
+               (concat ";;;###autoload\n(defun " (regexp-quote cmd) " ")
+               src)))))
+
+(ert-deftest test-org-drill-entry-commands-are-interactive ()
+  "Every command in the autoload list is actually an interactive command."
+  (dolist (cmd test-org-drill-autoloaded-commands)
+    (should (commandp (intern cmd)))))
+
+(provide 'test-org-drill-autoloads)
+
+;;; test-org-drill-autoloads.el ends here
diff --git a/tests/test-org-drill-current-scope.el b/tests/test-org-drill-current-scope.el
new file mode 100644
index 0000000..9743c5f
--- /dev/null
+++ b/tests/test-org-drill-current-scope.el
@@ -0,0 +1,48 @@
+;;; test-org-drill-current-scope.el --- Tests for org-drill-current-scope  -*- lexical-binding: t; -*-
+
+;;; Commentary:
+;; org-drill-current-scope translates a drill scope into the scope argument
+;; org-map-entries expects, and org-drill-map-entries delegates to it.  The
+;; map-entries mapping itself and drill-match filtering are covered in
+;; test-org-drill.el (find-entries / find-tagged-entries); this file covers
+;; the scope-translation branches, which had no tests.
+
+;;; Code:
+
+(require 'ert)
+(require 'cl-lib)
+(require 'org-drill)
+
+(ert-deftest test-org-drill-current-scope-file-returns-nil ()
+  "Scope `file' maps to nil — the current buffer, respecting narrowing."
+  (should (null (org-drill-current-scope 'file))))
+
+(ert-deftest test-org-drill-current-scope-file-no-restriction-returns-file ()
+  "Scope `file-no-restriction' maps to `file' — whole buffer, ignoring narrowing."
+  (should (eq 'file (org-drill-current-scope 'file-no-restriction))))
+
+(ert-deftest test-org-drill-current-scope-custom-symbol-passes-through ()
+  "An unrecognized scope such as `tree' is returned unchanged."
+  (should (eq 'tree (org-drill-current-scope 'tree))))
+
+(ert-deftest test-org-drill-current-scope-nil-falls-back-to-org-drill-scope ()
+  "A nil scope falls back to the value of `org-drill-scope'."
+  (let ((org-drill-scope 'tree))
+    (should (eq 'tree (org-drill-current-scope nil)))))
+
+(ert-deftest test-org-drill-current-scope-directory-lists-org-files ()
+  "Scope `directory' returns the .org files in the current file's directory."
+  (let (captured-dir)
+    (cl-letf (((symbol-function 'buffer-file-name)
+               (lambda (&rest _) "/tmp/deck/cards.org"))
+              ((symbol-function 'directory-files)
+               (lambda (dir _full _match)
+                 (setq captured-dir dir)
+                 '("/tmp/deck/a.org" "/tmp/deck/b.org"))))
+      (let ((result (org-drill-current-scope 'directory)))
+        (should (equal "/tmp/deck/" captured-dir))
+        (should (equal '("/tmp/deck/a.org" "/tmp/deck/b.org") result))))))
+
+(provide 'test-org-drill-current-scope)
+
+;;; test-org-drill-current-scope.el ends here
diff --git a/tests/test-org-drill-determine-next-interval-sm2.el b/tests/test-org-drill-determine-next-interval-sm2.el
index 622744d..3bf5cf3 100644
--- a/tests/test-org-drill-determine-next-interval-sm2.el
+++ b/tests/test-org-drill-determine-next-interval-sm2.el
@@ -417,5 +417,26 @@ Simulates inconsistent learning."
     (should (= interval-2 -1))
     (should (= failures-2 1))))
 
+;;; Error Cases - cl-assert invariant violations
+
+;; The function asserts (> n 0) and (and (>= quality 0) (<= quality 5)).
+;; n is normalized from 0 to 1 first, so only a negative n trips its assert.
+
+(ert-deftest test-org-drill-determine-next-interval-sm2-error-quality-above-max ()
+  "Quality above the 0-5 range trips the quality assertion."
+  (should-error (org-drill-determine-next-interval-sm2 1 2 2.5 6 0 4.0 1)
+                :type 'cl-assertion-failed))
+
+(ert-deftest test-org-drill-determine-next-interval-sm2-error-quality-below-min ()
+  "Quality below the 0-5 range trips the quality assertion."
+  (should-error (org-drill-determine-next-interval-sm2 1 2 2.5 -1 0 4.0 1)
+                :type 'cl-assertion-failed))
+
+(ert-deftest test-org-drill-determine-next-interval-sm2-error-negative-n ()
+  "A negative repeat count trips the (> n 0) assertion.  Note n=0 is
+normalized to 1 before the assert, so zero is not an error case."
+  (should-error (org-drill-determine-next-interval-sm2 1 -1 2.5 4 0 4.0 1)
+                :type 'cl-assertion-failed))
+
 (provide 'test-org-drill-determine-next-interval-sm2)
 ;;; test-org-drill-determine-next-interval-sm2.el ends here
diff --git a/tests/test-org-drill-final-helpers.el b/tests/test-org-drill-final-helpers.el
index c9cb0a3..b09efb7 100644
--- a/tests/test-org-drill-final-helpers.el
+++ b/tests/test-org-drill-final-helpers.el
@@ -111,8 +111,8 @@ matches leitner-tagged entries)."
         (should (null org-drill-leitner-boxed-entries))
         (should (null org-drill-leitner-unboxed-entries))))))
 
-(ert-deftest test-map-leitner-capture-non-drill-entry-skipped ()
-  "Non-drill entries (no :drill: tag inheritance) are skipped silently."
+(ert-deftest test-map-leitner-capture-untagged-heading-skipped ()
+  "A heading carrying no drill/leitner tag is skipped silently."
   (with-org-buffer "* Plain heading\n"
     (let ((session (org-drill-session))
           (org-drill-leitner-boxed-entries nil)
diff --git a/tests/test-org-drill-language-presenters.el b/tests/test-org-drill-language-presenters.el
index 6375b5f..da0a3a8 100644
--- a/tests/test-org-drill-language-presenters.el
+++ b/tests/test-org-drill-language-presenters.el
@@ -154,6 +154,25 @@
          (lambda (_) (setq reschedule-called t))))
       (should reschedule-called))))
 
+;;;; org-drill--format-tense-mood
+
+(ert-deftest test-org-drill-format-tense-mood-both ()
+  "With both tense and mood, the label names both."
+  (should (equal "past tense, subjunctive mood"
+                 (org-drill--format-tense-mood "past" "subjunctive"))))
+
+(ert-deftest test-org-drill-format-tense-mood-tense-only ()
+  "With only a tense, the label names the tense."
+  (should (equal "present tense" (org-drill--format-tense-mood "present" nil))))
+
+(ert-deftest test-org-drill-format-tense-mood-mood-only ()
+  "With only a mood, the label names the mood."
+  (should (equal "imperative mood" (org-drill--format-tense-mood nil "imperative"))))
+
+(ert-deftest test-org-drill-format-tense-mood-neither-is-nil ()
+  "With neither tense nor mood, there is no label."
+  (should (null (org-drill--format-tense-mood nil nil))))
+
 (provide 'test-org-drill-language-presenters)
 
 ;;; test-org-drill-language-presenters.el ends here
diff --git a/tests/test-org-drill-map-leitner-capture.el b/tests/test-org-drill-map-leitner-capture.el
index bc43c7d..114f51e 100644
--- a/tests/test-org-drill-map-leitner-capture.el
+++ b/tests/test-org-drill-map-leitner-capture.el
@@ -60,8 +60,8 @@
       (should (= 0 (length org-drill-leitner-boxed-entries)))
       (should (= 0 (length org-drill-leitner-unboxed-entries))))))
 
-(ert-deftest test-map-leitner-capture-non-drill-entry-skipped ()
-  "Non-drill heading is skipped entirely."
+(ert-deftest test-map-leitner-capture-no-headline-skipped ()
+  "A buffer with no headline at all is skipped entirely."
   (with-leitner-tempfile "Just text, no headlines\n"
     (let ((session (org-drill-session))
           (org-drill-question-tag org-drill-leitner-tag))
diff --git a/tests/test-org-drill-multicloze-dispatch.el b/tests/test-org-drill-multicloze-dispatch.el
index e871105..99861c7 100644
--- a/tests/test-org-drill-multicloze-dispatch.el
+++ b/tests/test-org-drill-multicloze-dispatch.el
@@ -138,6 +138,68 @@ piece is guaranteed not to be the first)."
                (args (cdr call)))
           (should (eq -1 (nth 1 args))))))))
 
+;;;; Basic variants — delegation contract
+;;
+;; hide1/hide2/hide-first/hide-last are thin wrappers.  The hiding
+;; mechanics they delegate to (hide-n / hide-nth) are exercised directly
+;; in test-org-drill-multicloze-hiding.el, so re-driving present-and-reveal
+;; here would just re-test those.  What's untested is the wiring: which
+;; delegate each variant calls and with what argument.
+
+(ert-deftest test-multicloze-hide1-delegates-to-hide-n-1 ()
+  "hide1 hides one piece: delegates to hide-n with number-to-hide = 1."
+  (with-fresh-drill-entry
+    (let (recorded)
+      (cl-letf (((symbol-function 'org-drill-present-multicloze-hide-n)
+                 (lambda (_session n &rest _) (setq recorded n) t)))
+        (org-drill-present-multicloze-hide1 (org-drill-session))
+        (should (eql 1 recorded))))))
+
+(ert-deftest test-multicloze-hide2-delegates-to-hide-n-2 ()
+  "hide2 hides two pieces: delegates to hide-n with number-to-hide = 2."
+  (with-fresh-drill-entry
+    (let (recorded)
+      (cl-letf (((symbol-function 'org-drill-present-multicloze-hide-n)
+                 (lambda (_session n &rest _) (setq recorded n) t)))
+        (org-drill-present-multicloze-hide2 (org-drill-session))
+        (should (eql 2 recorded))))))
+
+(ert-deftest test-multicloze-hide-first-delegates-to-hide-nth-1 ()
+  "hide-first hides the first piece: delegates to hide-nth with 1."
+  (with-fresh-drill-entry
+    (let (recorded)
+      (cl-letf (((symbol-function 'org-drill-present-multicloze-hide-nth)
+                 (lambda (_session nth &rest _) (setq recorded nth) t)))
+        (org-drill-present-multicloze-hide-first (org-drill-session))
+        (should (eql 1 recorded))))))
+
+(ert-deftest test-multicloze-hide-last-delegates-to-hide-nth-last ()
+  "hide-last hides the last piece: delegates to hide-nth with -1."
+  (with-fresh-drill-entry
+    (let (recorded)
+      (cl-letf (((symbol-function 'org-drill-present-multicloze-hide-nth)
+                 (lambda (_session nth &rest _) (setq recorded nth) t)))
+        (org-drill-present-multicloze-hide-last (org-drill-session))
+        (should (eql -1 recorded))))))
+
+(ert-deftest test-multicloze-show1-delegates-to-hide-n-minus-1 ()
+  "show1 reveals one piece (hides the rest): delegates to hide-n with -1."
+  (with-fresh-drill-entry
+    (let (recorded)
+      (cl-letf (((symbol-function 'org-drill-present-multicloze-hide-n)
+                 (lambda (_session n &rest _) (setq recorded n) t)))
+        (org-drill-present-multicloze-show1 (org-drill-session))
+        (should (eql -1 recorded))))))
+
+(ert-deftest test-multicloze-show2-delegates-to-hide-n-minus-2 ()
+  "show2 reveals two pieces: delegates to hide-n with -2."
+  (with-fresh-drill-entry
+    (let (recorded)
+      (cl-letf (((symbol-function 'org-drill-present-multicloze-hide-n)
+                 (lambda (_session n &rest _) (setq recorded n) t)))
+        (org-drill-present-multicloze-show2 (org-drill-session))
+        (should (eql -2 recorded))))))
+
 (provide 'test-org-drill-multicloze-dispatch)
 
 ;;; test-org-drill-multicloze-dispatch.el ends here
diff --git a/tests/test-org-drill-spanish-and-top-level.el b/tests/test-org-drill-spanish-and-top-level.el
index 61fc546..465d82f 100644
--- a/tests/test-org-drill-spanish-and-top-level.el
+++ b/tests/test-org-drill-spanish-and-top-level.el
@@ -88,6 +88,48 @@ hablo, hablas, ...
         (org-drill-present-spanish-verb (org-drill-session))
         (should (string-match-p "future perfect" shown-prompt))))))
 
+(ert-deftest test-present-spanish-verb-branch-1-present-tense-conjugate ()
+  "Branch 1 reveals the English side and asks to conjugate the present tense."
+  (with-card-buffer "* Verb :drill:\n** Infinitive\nhablar\n** English\nto speak\n** Present Tense\nfoo\n"
+    (let ((shown-prompt nil))
+      (cl-letf (((symbol-function 'cl-random) (lambda (_) 1))
+                ((symbol-function 'org-drill-presentation-prompt)
+                 (lambda (_session &optional prompt &rest _)
+                   (setq shown-prompt prompt) t))
+                ((symbol-function 'org-drill--show-latex-fragments) #'ignore)
+                ((symbol-function 'org-display-inline-images) #'ignore))
+        (org-drill-present-spanish-verb (org-drill-session))
+        (should (string-match-p "present.* tense" shown-prompt))
+        (should (string-match-p "English verb" shown-prompt))))))
+
+(ert-deftest test-present-spanish-verb-branch-3-past-tense-conjugate ()
+  "Branch 3 reveals the English side and asks to conjugate the past tense."
+  (with-card-buffer "* Verb :drill:\n** Infinitive\nhablar\n** English\nto speak\n** Past Tense\nfoo\n"
+    (let ((shown-prompt nil))
+      (cl-letf (((symbol-function 'cl-random) (lambda (_) 3))
+                ((symbol-function 'org-drill-presentation-prompt)
+                 (lambda (_session &optional prompt &rest _)
+                   (setq shown-prompt prompt) t))
+                ((symbol-function 'org-drill--show-latex-fragments) #'ignore)
+                ((symbol-function 'org-display-inline-images) #'ignore))
+        (org-drill-present-spanish-verb (org-drill-session))
+        (should (string-match-p "past.* tense" shown-prompt))
+        (should (string-match-p "English verb" shown-prompt))))))
+
+(ert-deftest test-present-spanish-verb-branch-5-future-perfect-conjugate ()
+  "Branch 5 reveals the English side and asks to conjugate the future perfect."
+  (with-card-buffer "* Verb :drill:\n** Infinitive\nhablar\n** English\nto speak\n** Future Perfect Tense\nfoo\n"
+    (let ((shown-prompt nil))
+      (cl-letf (((symbol-function 'cl-random) (lambda (_) 5))
+                ((symbol-function 'org-drill-presentation-prompt)
+                 (lambda (_session &optional prompt &rest _)
+                   (setq shown-prompt prompt) t))
+                ((symbol-function 'org-drill--show-latex-fragments) #'ignore)
+                ((symbol-function 'org-display-inline-images) #'ignore))
+        (org-drill-present-spanish-verb (org-drill-session))
+        (should (string-match-p "future perfect" shown-prompt))
+        (should (string-match-p "English verb" shown-prompt))))))
+
 ;;;; org-drill-cram and friends
 
 (ert-deftest test-org-drill-cram-passes-cram-flag ()
diff --git a/tests/test-org-drill-utilities-and-leitner.el b/tests/test-org-drill-utilities-and-leitner.el
index cc0157c..02761a2 100644
--- a/tests/test-org-drill-utilities-and-leitner.el
+++ b/tests/test-org-drill-utilities-and-leitner.el
@@ -61,6 +61,12 @@
 (ert-deftest test-org-drill-shuffle-single-element-unchanged ()
   (should (equal '(42) (org-drill-shuffle (list 42)))))
 
+(ert-deftest test-org-drill-shuffle-rejects-non-list ()
+  "The argument must be a list.  A non-list (number, vector) is rejected
+with a clear type error rather than silently coerced."
+  (should-error (org-drill-shuffle 42) :type 'wrong-type-argument)
+  (should-error (org-drill-shuffle [1 2 3]) :type 'wrong-type-argument))
+
 ;;;; org-drill-pop-random (macro)
 
 (ert-deftest test-org-drill-pop-random-removes-one-element ()
diff --git a/tests/test-org-drill-version.el b/tests/test-org-drill-version.el
new file mode 100644
index 0000000..4dc71d3
--- /dev/null
+++ b/tests/test-org-drill-version.el
@@ -0,0 +1,28 @@
+;;; test-org-drill-version.el --- Tests for org-drill-version  -*- lexical-binding: t; -*-
+
+;;; Commentary:
+;; org-drill-version is both a constant (the package version string) and an
+;; interactive command that reports it, so bug reporters don't have to open
+;; the file header.
+
+;;; Code:
+
+(require 'ert)
+(require 'org-drill)
+
+(ert-deftest test-org-drill-version-is-a-version-string ()
+  "The constant is a non-empty dotted version string."
+  (should (stringp org-drill-version))
+  (should (string-match-p "\\`[0-9]+\\.[0-9]+" org-drill-version)))
+
+(ert-deftest test-org-drill-version-command-returns-the-version ()
+  "Calling the command returns the version string."
+  (should (equal org-drill-version (org-drill-version))))
+
+(ert-deftest test-org-drill-version-command-is-interactive ()
+  "The version reporter is an interactive command."
+  (should (commandp 'org-drill-version)))
+
+(provide 'test-org-drill-version)
+
+;;; test-org-drill-version.el ends here