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diff --git a/tests/test-debug-wttrin-enable.el b/tests/test-debug-wttrin-enable.el
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+;;; test-debug-wttrin-enable.el --- Tests for debug-wttrin-enable -*- lexical-binding: t; -*-
+
+;; Copyright (C) 2025-2026 Craig Jennings
+
+;;; Commentary:
+
+;; Unit tests for debug-wttrin-enable.  Verifies the interactive command
+;; flips `wttrin-debug' to t and is idempotent when already enabled.
+
+;;; Code:
+
+(require 'ert)
+(require 'wttrin)
+(require 'testutil-wttrin)
+
+(require 'wttrin-debug
+         (expand-file-name "wttrin-debug.el"
+                           (file-name-directory (locate-library "wttrin"))))
+
+;;; Normal Cases
+
+(ert-deftest test-debug-wttrin-enable-normal-flips-from-nil-to-t ()
+  "Calling enable when wttrin-debug is nil sets it to t."
+  (let ((wttrin-debug nil))
+    (debug-wttrin-enable)
+    (should (eq wttrin-debug t))))
+
+(ert-deftest test-debug-wttrin-enable-normal-idempotent-when-already-enabled ()
+  "Calling enable when wttrin-debug is already t leaves it t."
+  (let ((wttrin-debug t))
+    (debug-wttrin-enable)
+    (should (eq wttrin-debug t))))
+
+;;; Boundary Cases
+
+(ert-deftest test-debug-wttrin-enable-boundary-overrides-non-boolean-truthy-value ()
+  "Calling enable replaces a non-boolean truthy value with t."
+  (let ((wttrin-debug 'verbose))
+    (debug-wttrin-enable)
+    (should (eq wttrin-debug t))))
+
+(provide 'test-debug-wttrin-enable)
+;;; test-debug-wttrin-enable.el ends here