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+;;; test-chime-async-injection.el --- Tests for async environment injection -*- lexical-binding: t; -*-
+
+;; Copyright (C) 2024-2026 Craig Jennings
+
+;; Author: Craig Jennings <c@cjennings.net>
+
+;; This program is free software: you can redistribute it and/or modify
+;; it under the terms of the GNU General Public License as published by
+;; the Free Software Foundation, either version 3 of the License, or
+;; (at your option) any later version.
+
+;; This program is distributed in the hope that it will be useful,
+;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;; GNU General Public License for more details.
+
+;;; Commentary:
+
+;; Tests that every chime defcustom the async child reads is injected into
+;; the child by `chime--environment-regex'.
+;;
+;; The child calls (require 'chime), so an uninjected defcustom is still
+;; *bound* there -- at its default.  A user who customizes it sees no error
+;; and no effect, which is the worst shape a bug can take.  That is exactly
+;; what happened to chime-tooltip-lookahead-hours: the docstring invites
+;; 8760 "to see distant events", and the child kept fetching 168 hours.
+;;
+;; The load-bearing test walks the child form and fails on any chime
+;; defcustom it reads that the regex doesn't cover, so a variable added to
+;; the child later cannot reintroduce the bug quietly.
+
+;;; Code:
+
+(require 'test-bootstrap (expand-file-name "test-bootstrap.el"))
+
+;;; Helpers
+
+(defun test-chime-injection--symbols (form)
+  "Return every symbol appearing anywhere in FORM."
+  (cond
+   ((symbolp form) (and form (list form)))
+   ((consp form) (append (test-chime-injection--symbols (car form))
+                         (test-chime-injection--symbols (cdr form))))
+   (t nil)))
+
+(defun test-chime-injection--chime-defcustoms (form)
+  "Return the chime defcustoms appearing in FORM, deduplicated."
+  (seq-uniq
+   (seq-filter (lambda (sym)
+                 (and (custom-variable-p sym)
+                      (string-prefix-p "chime-" (symbol-name sym))))
+               (test-chime-injection--symbols form))))
+
+;;; Normal Cases
+
+(ert-deftest test-chime-async-injection-covers-every-chime-defcustom-in-the-child ()
+  "Every chime defcustom the async child reads is injected into it.
+An uninjected one silently runs at its default in the child, so a user's
+customization is ignored without any error."
+  (let* ((form (chime--retrieve-events))
+         (regex (chime--environment-regex))
+         (uncovered (seq-remove
+                     (lambda (sym) (string-match-p regex (symbol-name sym)))
+                     (test-chime-injection--chime-defcustoms form))))
+    (should-not uncovered)))
+
+(ert-deftest test-chime-async-injection-covers-the-lookahead-variables ()
+  "Both lookahead variables reach the child.
+The child sizes its agenda span from them, so without injection it fetches
+the default 168-hour window no matter what the user set."
+  (let ((regex (chime--environment-regex)))
+    (should (string-match-p regex "chime-modeline-lookahead-minutes"))
+    (should (string-match-p regex "chime-tooltip-lookahead-hours"))))
+
+(ert-deftest test-chime-async-injection-covers-the-pre-existing-variables ()
+  "The variables injected before the lookahead fix still are."
+  (let ((regex (chime--environment-regex)))
+    (dolist (name '("org-agenda-files" "load-path" "org-todo-keywords"
+                    "chime-alert-intervals" "chime-include-filters"
+                    "chime-exclude-filters"))
+      (should (string-match-p regex name)))))
+
+;;; Boundary Cases
+
+(ert-deftest test-chime-async-injection-regex-is-anchored ()
+  "The regex matches whole variable names, not substrings.
+Without anchoring, a user's unrelated `my-org-agenda-files-backup' would
+be swept into the child."
+  (let ((regex (chime--environment-regex)))
+    (should-not (string-match-p regex "my-org-agenda-files"))
+    (should-not (string-match-p regex "org-agenda-files-extra"))))
+
+(ert-deftest test-chime-async-injection-honors-additional-regexes ()
+  "`chime-additional-environment-regexes' extends the injected set."
+  (let* ((chime-additional-environment-regexes '("\\`my-var\\'"))
+         (regex (chime--environment-regex)))
+    (should (string-match-p regex "my-var"))
+    (should (string-match-p regex "org-agenda-files"))))
+
+(provide 'test-chime-async-injection)
+;;; test-chime-async-injection.el ends here