1 files changed, 83 insertions, 0 deletions
diff --git a/tests/test-config-utilities-format-build-time.el b/tests/test-config-utilities-format-build-time.el
new file mode 100644
index 00000000..70473e2d
--- /dev/null
+++ b/tests/test-config-utilities-format-build-time.el
@@ -0,0 +1,83 @@
+;;; test-config-utilities-format-build-time.el --- Tests for cj/emacs-build--format-build-time -*- lexical-binding: t; -*-
+
+;;; Commentary:
+;; Tests for cj/emacs-build--format-build-time from config-utilities.el.
+;;
+;; Pure function that converts various time value representations to a
+;; human-readable string. Branches on input type: nil, string, cons of
+;; integers (Emacs time value), number (epoch seconds), and fallback.
+
+;;; Code:
+
+(require 'ert)
+
+(add-to-list 'load-path (expand-file-name "modules" user-emacs-directory))
+(require 'config-utilities)
+
+;;; Normal Cases
+
+(ert-deftest test-config-utilities-format-build-time-normal-nil-returns-unknown ()
+  "Nil input should return \"unknown\"."
+  (should (equal (cj/emacs-build--format-build-time nil) "unknown")))
+
+(ert-deftest test-config-utilities-format-build-time-normal-string-returned-as-is ()
+  "String input should be returned unchanged."
+  (should (equal (cj/emacs-build--format-build-time "2026-01-15 10:30:00 CST")
+                 "2026-01-15 10:30:00 CST")))
+
+(ert-deftest test-config-utilities-format-build-time-normal-cons-formats-timestamp ()
+  "Cons of integers (Emacs time value) should produce formatted date string."
+  (let* ((time-val (encode-time 0 30 14 15 2 2026))
+         (result (cj/emacs-build--format-build-time time-val)))
+    (should (string-match-p "2026-02-15" result))
+    (should (string-match-p "14:30:00" result))))
+
+(ert-deftest test-config-utilities-format-build-time-normal-number-formats-timestamp ()
+  "Numeric epoch seconds should produce formatted date string."
+  (let* ((time-val (float-time (encode-time 0 30 14 15 2 2026)))
+         (result (cj/emacs-build--format-build-time time-val)))
+    (should (string-match-p "2026-02-15" result))
+    (should (string-match-p "14:30:00" result))))
+
+(ert-deftest test-config-utilities-format-build-time-normal-fallback-formats-with-format ()
+  "Unrecognized types should be stringified via `format'."
+  (should (equal (cj/emacs-build--format-build-time 'some-symbol) "some-symbol")))
+
+;;; Boundary Cases
+
+(ert-deftest test-config-utilities-format-build-time-boundary-empty-string ()
+  "Empty string input should be returned as empty string."
+  (should (equal (cj/emacs-build--format-build-time "") "")))
+
+(ert-deftest test-config-utilities-format-build-time-boundary-zero-epoch ()
+  "Zero epoch (Unix epoch start) should produce a valid formatted date string."
+  (let ((result (cj/emacs-build--format-build-time 0)))
+    (should (stringp result))
+    (should (string-match-p "19[67][0-9]" result))))
+
+(ert-deftest test-config-utilities-format-build-time-boundary-integer-epoch ()
+  "Integer (not float) epoch should be handled by numberp branch."
+  (let* ((time-val (truncate (float-time (encode-time 0 0 12 1 1 2025))))
+         (result (cj/emacs-build--format-build-time time-val)))
+    (should (string-match-p "2025-01-01" result))
+    (should (string-match-p "12:00:00" result))))
+
+(ert-deftest test-config-utilities-format-build-time-boundary-cons-not-integers ()
+  "Cons where car is not integer should hit the fallback branch."
+  (let ((result (cj/emacs-build--format-build-time '("not" "integers"))))
+    (should (equal result "(not integers)"))))
+
+(ert-deftest test-config-utilities-format-build-time-boundary-vector-fallback ()
+  "Vector input should hit the fallback branch."
+  (should (equal (cj/emacs-build--format-build-time [1 2 3]) "[1 2 3]")))
+
+(ert-deftest test-config-utilities-format-build-time-boundary-cons-and-number-agree ()
+  "Cons time value and its float-time equivalent should produce the same output."
+  (let* ((cons-time (encode-time 0 30 14 15 2 2026))
+         (num-time (float-time cons-time))
+         (result-cons (cj/emacs-build--format-build-time cons-time))
+         (result-num (cj/emacs-build--format-build-time num-time)))
+    (should (equal result-cons result-num))))
+
+(provide 'test-config-utilities-format-build-time)
+;;; test-config-utilities-format-build-time.el ends here