test(config-utilities): cover validate-timestamps and format-report helpers

Two test files covering the extracted timestamp-validation helpers.

cj/--validate-timestamps-in-buffer (8 tests): empty buffer no-op,
buffer with no timestamps, buffer with all valid timestamps,
DEADLINE flagged with "DEADLINE" property, SCHEDULED flagged with
"SCHEDULED", inline-timestamp flagged with "inline timestamp",
multiple invalid collected in document order, mixed valid+invalid
returning only the invalid one. Tests use real org parsing and
mock org-time-string-to-absolute at the boundary so an arbitrary
timestamp can be marked invalid for a given test.

cj/--format-validation-report-section (4 tests): no-entries says
"No invalid timestamps found", single-entry produces the file: link
+ Property/Type + Invalid timestamp lines, multiple-entry preserves
input order, every section ends with a trailing blank line.

1 files changed, 130 insertions, 0 deletions

diff --git a/tests/test-config-utilities--validate-timestamps-in-buffer.el b/tests/test-config-utilities--validate-timestamps-in-buffer.el
new file mode 100644
index 00000000..8ca51a55
--- /dev/null
+++ b/tests/test-config-utilities--validate-timestamps-in-buffer.el
@@ -0,0 +1,130 @@
+;;; test-config-utilities--validate-timestamps-in-buffer.el --- Tests for cj/--validate-timestamps-in-buffer -*- lexical-binding: t; -*-
+
+;;; Commentary:
+;; Tests for `cj/--validate-timestamps-in-buffer'.  The function walks
+;; an org buffer's headlines, checks DEADLINE/SCHEDULED/TIMESTAMP
+;; properties plus inline timestamps, and returns a list of tuples
+;; for every timestamp where `org-time-string-to-absolute' returns
+;; nil.  Tests use real org parsing on real timestamps and mock the
+;; validator at the boundary so an arbitrary timestamp can be marked
+;; invalid for the test.
+
+;;; Code:
+
+(require 'ert)
+(require 'cl-lib)
+
+(add-to-list 'load-path (expand-file-name "modules" user-emacs-directory))
+(require 'config-utilities)
+(require 'org)
+(require 'org-element)
+
+(defmacro test-config-utilities--with-org-buffer (content &rest body)
+  "Run BODY in a temp buffer holding CONTENT in `org-mode'."
+  (declare (indent 1) (debug t))
+  `(with-temp-buffer
+     (let ((org-mode-hook nil))
+       (insert ,content)
+       (org-mode)
+       ,@body)))
+
+(defmacro test-config-utilities--with-invalid-timestamps (invalid-set &rest body)
+  "Run BODY with `org-time-string-to-absolute' returning nil for any
+timestamp string in INVALID-SET, normal behaviour otherwise."
+  (declare (indent 1) (debug t))
+  `(let ((--invalid-set ,invalid-set)
+         (--orig (symbol-function 'org-time-string-to-absolute)))
+     (cl-letf (((symbol-function 'org-time-string-to-absolute)
+                (lambda (s &rest args)
+                  (if (member s --invalid-set)
+                      (error "test-mocked invalid timestamp: %s" s)
+                    (apply --orig s args)))))
+       ,@body)))
+
+(ert-deftest test-config-utilities-validate-buffer-no-timestamps-returns-empty ()
+  "Boundary: a buffer with no timestamps returns an empty list."
+  (test-config-utilities--with-org-buffer "* Heading\nJust prose.\n"
+    (should-not (cj/--validate-timestamps-in-buffer "/x.org"))))
+
+(ert-deftest test-config-utilities-validate-buffer-empty-buffer-returns-empty ()
+  "Boundary: an empty buffer returns an empty list."
+  (test-config-utilities--with-org-buffer ""
+    (should-not (cj/--validate-timestamps-in-buffer "/x.org"))))
+
+(ert-deftest test-config-utilities-validate-buffer-valid-timestamps-returns-empty ()
+  "Normal: every valid timestamp passes; the result is empty."
+  (test-config-utilities--with-org-buffer
+      "* Headline
+DEADLINE: <2026-04-30 Thu>
+"
+    (should-not (cj/--validate-timestamps-in-buffer "/x.org"))))
+
+(ert-deftest test-config-utilities-validate-buffer-deadline-flagged-when-invalid ()
+  "Normal: an invalid DEADLINE is flagged with property \"DEADLINE\"."
+  (test-config-utilities--with-org-buffer
+      "* Bad
+DEADLINE: <2026-04-30 Thu>
+"
+    (test-config-utilities--with-invalid-timestamps '("<2026-04-30 Thu>")
+      (let ((result (cj/--validate-timestamps-in-buffer "/x.org")))
+        (should (= 1 (length result)))
+        (cl-destructuring-bind (file _pos head prop ts) (car result)
+          (should (equal file "/x.org"))
+          (should (equal head "Bad"))
+          (should (equal prop "DEADLINE"))
+          (should (equal ts "<2026-04-30 Thu>")))))))
+
+(ert-deftest test-config-utilities-validate-buffer-scheduled-flagged-when-invalid ()
+  "Normal: an invalid SCHEDULED is flagged with property \"SCHEDULED\"."
+  (test-config-utilities--with-org-buffer
+      "* Sched
+SCHEDULED: <2026-05-01 Fri>
+"
+    (test-config-utilities--with-invalid-timestamps '("<2026-05-01 Fri>")
+      (let ((result (cj/--validate-timestamps-in-buffer "/x.org")))
+        (should (= 1 (length result)))
+        (should (equal "SCHEDULED" (nth 3 (car result))))))))
+
+(ert-deftest test-config-utilities-validate-buffer-inline-flagged-as-inline ()
+  "Normal: an invalid inline timestamp in headline contents is flagged
+with property \"inline timestamp\"."
+  (test-config-utilities--with-org-buffer
+      "* Body has timestamp
+Some prose mentioning <2026-06-01 Mon> in passing.
+"
+    (test-config-utilities--with-invalid-timestamps '("<2026-06-01 Mon>")
+      (let ((result (cj/--validate-timestamps-in-buffer "/x.org")))
+        (should (= 1 (length result)))
+        (should (equal "inline timestamp" (nth 3 (car result))))))))
+
+(ert-deftest test-config-utilities-validate-buffer-multiple-invalid-collected-in-order ()
+  "Normal: multiple invalid timestamps are returned in document order."
+  (test-config-utilities--with-org-buffer
+      "* First
+DEADLINE: <2026-01-01 Thu>
+* Second
+SCHEDULED: <2026-02-02 Mon>
+"
+    (test-config-utilities--with-invalid-timestamps
+        '("<2026-01-01 Thu>" "<2026-02-02 Mon>")
+      (let ((result (cj/--validate-timestamps-in-buffer "/x.org")))
+        (should (= 2 (length result)))
+        (should (equal "First" (nth 2 (nth 0 result))))
+        (should (equal "Second" (nth 2 (nth 1 result))))))))
+
+(ert-deftest test-config-utilities-validate-buffer-mixed-valid-and-invalid ()
+  "Boundary: buffer with one valid and one invalid timestamp returns
+only the invalid one."
+  (test-config-utilities--with-org-buffer
+      "* Good
+DEADLINE: <2026-04-30 Thu>
+* Bad
+DEADLINE: <2026-12-25 Fri>
+"
+    (test-config-utilities--with-invalid-timestamps '("<2026-12-25 Fri>")
+      (let ((result (cj/--validate-timestamps-in-buffer "/x.org")))
+        (should (= 1 (length result)))
+        (should (equal "Bad" (nth 2 (car result))))))))
+
+(provide 'test-config-utilities--validate-timestamps-in-buffer)
+;;; test-config-utilities--validate-timestamps-in-buffer.el ends here