test: close coverage gaps from the preceding batch

Untested paths surfaced while reviewing the preceding feature/fix commits:
- calendar-sync: a test that `-L' precedes `-l' in the worker command (separate `member' checks wouldn't catch a swap), plus a `:slow' tag on the real-subprocess worker test so it stays out of the default `make test' run.
- org-capture cache: a killed marker buffer invalidates the entry and the next resolution rescans without erroring on the stale marker, `cj/org-capture-clear-target-cache' actually empties the hash, and non-`file+headline' targets (`file', `file+olp', `file+function') fall through to the original `org-capture-set-target-location'.
- lorem-optimum: `cj/lipsum-title' on an empty chain returns "", not an error.
- calibredb-epub: a negative `cj/nov-margin-percent' is clamped up to 0 (text takes the full window width).
- mu4e attachments: the default save directory comes from the part's `:target-dir' and falls back to `~/Downloads/', and asking for the attachment at point on a header line fails with a `user-error'.

1 files changed, 13 insertions, 0 deletions

diff --git a/tests/test-calendar-sync-async-worker.el b/tests/test-calendar-sync-async-worker.el
index 6701df85..3bf803ec 100644
--- a/tests/test-calendar-sync-async-worker.el
+++ b/tests/test-calendar-sync-async-worker.el
@@ -37,8 +37,21 @@
                             (string-match-p "'(\"me@example\\.test\")" arg)))
                      command))))
 
+(ert-deftest test-calendar-sync--worker-command-puts-L-before-l ()
+  "Order: `-L module-dir' must precede `-l calendar-sync.el' so the sibling
+load-path entry is in effect by the time the module load runs.  Asserting both
+via `member' separately wouldn't catch a swap."
+  (let* ((calendar-sync--module-file "/tmp/calendar-sync.el")
+         (calendar-sync-past-months 2)
+         (calendar-sync-future-months 6)
+         (calendar-sync-user-emails '("me@example.test"))
+         (command (calendar-sync--worker-command "/tmp/input.ics" "/tmp/output.org")))
+    (should (< (cl-position "-L" command :test #'equal)
+               (cl-position "-l" command :test #'equal)))))
+
 (ert-deftest test-calendar-sync--worker-command-loads-sibling-modules-without-init ()
   "The worker command should load calendar-sync and sibling modules without init."
+  :tags '(:slow)
   (let* ((calendar-sync--module-file
           (expand-file-name "modules/calendar-sync.el" user-emacs-directory))
          (command (append