fix(test-runner): reject a sibling dir that shares the test dir's prefix

cj/test--do-focus-add-file tested containment with a bare string-prefix-p on two truenames, so tests-old/foo.el passed as being inside tests/ and joined the focus list.

The correct helper was already there. cj/test--file-in-directory-p wraps the directory in file-name-as-directory first, and the other two call sites already used it. This one didn't.

The helper even had a sibling-rejection test. It was proven correct while the call site two hundred lines away never called it, which is why the new test drives the real focus-add path with a tests-old/ directory on disk rather than testing the helper again.

1 files changed, 4 insertions, 1 deletions

diff --git a/modules/test-runner.el b/modules/test-runner.el
index e05145e4..7f157f1c 100644
--- a/modules/test-runner.el
+++ b/modules/test-runner.el
@@ -239,7 +239,10 @@ Returns: \\='success if added successfully,
 Second value is the relative filename if successful."
   (cond
    ((null filepath) (cons 'no-file nil))
-   ((not (string-prefix-p (file-truename testdir) (file-truename filepath)))
+   ;; Route through the helper: it appends the trailing slash, so a sibling
+   ;; sharing the directory's name prefix (tests-old/ against tests/) is
+   ;; rejected.  A bare `string-prefix-p' on the truenames accepts it.
+   ((not (cj/test--file-in-directory-p filepath testdir))
     (cons 'not-in-testdir nil))
    (t
     (let ((relative (file-relative-name filepath testdir)))