fix: Mock file-writable-p in not-writable test

The previous test relied on file permissions (mode 444) to make
file-writable-p return nil. However, with-temp-file writes to a
temp file and renames, which succeeds if you own the file,
causing file-writable-p to still return t.

Use spy-on to mock file-writable-p instead.

Author: hugoduncan

test/cider-repl-tests.el

@@ -329,10 +329,10 @@ PROPERTY should be a symbol of either 'text, 'ansi-context or
              (cider-repl-history-size 100))
         (unwind-protect
             (progn
-              ;; Create a read-only file
               (write-region "" nil history-file)
-              (set-file-modes history-file #o444)
+              ;; Mock file-writable-p to return nil for this specific file
+              (spy-on 'file-writable-p :and-call-fake
+                      (lambda (f) (not (string= f history-file))))
               (expect (cider-repl--history-write history-file)
                       :to-throw 'error))
-          (set-file-modes history-file #o644)
           (delete-directory temp-dir t))))))