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diff --git a/tests/test-wttrin-debug-show-log.el b/tests/test-wttrin-debug-show-log.el
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+;;; test-wttrin-debug-show-log.el --- Tests for wttrin-debug-show-log -*- lexical-binding: t; -*-
+
+;; Copyright (C) 2025-2026 Craig Jennings
+
+;;; Commentary:
+
+;; Unit tests for wttrin-debug-show-log.  Verifies the *wttrin-debug-log*
+;; buffer is created with the expected header, entry rendering, and the
+;; reversed (oldest-first) ordering used for human reading.
+
+;;; Code:
+
+(require 'ert)
+(require 'wttrin)
+(require 'testutil-wttrin)
+
+(require 'wttrin-debug
+         (expand-file-name "wttrin-debug.el"
+                           (file-name-directory (locate-library "wttrin"))))
+
+;;; Setup and Teardown
+
+(defun test-wttrin-debug-show-log-setup ()
+  "Setup for show-log tests."
+  (when (get-buffer "*wttrin-debug-log*")
+    (kill-buffer "*wttrin-debug-log*")))
+
+(defun test-wttrin-debug-show-log-teardown ()
+  "Teardown for show-log tests."
+  (when (get-buffer "*wttrin-debug-log*")
+    (kill-buffer "*wttrin-debug-log*")))
+
+;;; Normal Cases
+
+(ert-deftest test-wttrin-debug-show-log-normal-creates-display-buffer ()
+  "Show-log creates the *wttrin-debug-log* buffer."
+  (test-wttrin-debug-show-log-setup)
+  (unwind-protect
+      (let ((wttrin--debug-log nil))
+        (wttrin-debug-show-log)
+        (should (get-buffer "*wttrin-debug-log*")))
+    (test-wttrin-debug-show-log-teardown)))
+
+(ert-deftest test-wttrin-debug-show-log-normal-header-shows-entry-count ()
+  "Header reflects the number of entries currently in the log."
+  (test-wttrin-debug-show-log-setup)
+  (unwind-protect
+      (let ((wttrin--debug-log '(("00:00:03.000" . "c")
+                                 ("00:00:02.000" . "b")
+                                 ("00:00:01.000" . "a"))))
+        (wttrin-debug-show-log)
+        (with-current-buffer "*wttrin-debug-log*"
+          (should (string-match-p "Total entries: 3" (buffer-string)))))
+    (test-wttrin-debug-show-log-teardown)))
+
+(ert-deftest test-wttrin-debug-show-log-normal-renders-entries-with-timestamps ()
+  "Each entry appears as [timestamp] message in the display."
+  (test-wttrin-debug-show-log-setup)
+  (unwind-protect
+      (let ((wttrin--debug-log '(("12:34:56.789" . "hello world"))))
+        (wttrin-debug-show-log)
+        (with-current-buffer "*wttrin-debug-log*"
+          (should (string-match-p "\\[12:34:56\\.789\\] hello world"
+                                  (buffer-string)))))
+    (test-wttrin-debug-show-log-teardown)))
+
+(ert-deftest test-wttrin-debug-show-log-normal-entries-rendered-oldest-first ()
+  "Storage is newest-first (push); display reverses to oldest-first for reading."
+  (test-wttrin-debug-show-log-setup)
+  (unwind-protect
+      (let ((wttrin--debug-log '(("00:00:03.000" . "third")
+                                 ("00:00:02.000" . "second")
+                                 ("00:00:01.000" . "first"))))
+        (wttrin-debug-show-log)
+        (with-current-buffer "*wttrin-debug-log*"
+          (let* ((contents (buffer-string))
+                 (pos-first (string-match "first" contents))
+                 (pos-second (string-match "second" contents))
+                 (pos-third (string-match "third" contents)))
+            (should pos-first)
+            (should pos-second)
+            (should pos-third)
+            (should (< pos-first pos-second))
+            (should (< pos-second pos-third)))))
+    (test-wttrin-debug-show-log-teardown)))
+
+;;; Boundary Cases
+
+(ert-deftest test-wttrin-debug-show-log-boundary-empty-log-shows-placeholder ()
+  "Empty log renders the \"No log entries yet\" placeholder."
+  (test-wttrin-debug-show-log-setup)
+  (unwind-protect
+      (let ((wttrin--debug-log nil))
+        (wttrin-debug-show-log)
+        (with-current-buffer "*wttrin-debug-log*"
+          (should (string-match-p "(No log entries yet)" (buffer-string)))
+          (should (string-match-p "Total entries: 0" (buffer-string)))))
+    (test-wttrin-debug-show-log-teardown)))
+
+(provide 'test-wttrin-debug-show-log)
+;;; test-wttrin-debug-show-log.el ends here