test: extract message-capture helper into testutil

Five test files hand-rolled the same scaffolding to capture the echo-area message: a nil-initialized var, a cl-letf on message, and a lambda that stored the formatted string. Centralize it as testutil-wttrin-with-captured-message, which binds the var and captures the last message shown.

Behavior is unchanged. The full suite stays green. Sites that mock message for a different reason are left alone: the ones that silence it with #'ignore, and the one that accumulates every message into a list.

1 files changed, 4 insertions, 7 deletions

diff --git a/tests/test-wttrin-clear-cache.el b/tests/test-wttrin-clear-cache.el
index 8185c5f..784be4c 100644
--- a/tests/test-wttrin-clear-cache.el
+++ b/tests/test-wttrin-clear-cache.el
@@ -43,13 +43,10 @@
   "User should be told the cache was cleared."
   (test-wttrin-clear-cache-setup)
   (unwind-protect
-      (let ((displayed-message nil))
-        (cl-letf (((symbol-function 'message)
-                   (lambda (fmt &rest args)
-                     (setq displayed-message (apply #'format fmt args)))))
-          (wttrin-clear-cache)
-          (should displayed-message)
-          (should (string-match-p "cache cleared" displayed-message))))
+      (testutil-wttrin-with-captured-message displayed-message
+        (wttrin-clear-cache)
+        (should displayed-message)
+        (should (string-match-p "cache cleared" displayed-message)))
     (test-wttrin-clear-cache-teardown)))
 
 ;;; Boundary Cases