diff --git a/lisp/emacs-lisp/ert-x.el b/lisp/emacs-lisp/ert-x.el
index 622f5654b25..6569b8ccc87 100644
--- a/lisp/emacs-lisp/ert-x.el
+++ b/lisp/emacs-lisp/ert-x.el
@@ -177,6 +177,18 @@ test for `called-interactively' in the command will fail."
     (cl-assert (not unread-command-events) t)
     return-value))
 
+(defmacro ert-simulate-keys (keys &rest body)
+  "Execute BODY with KEYS as pseudo-interactive input."
+  (declare (debug t) (indent 1))
+  `(let ((unread-command-events
+          ;; Add some C-g to try and make sure we still exit
+          ;; in case something goes wrong.
+          (append ,keys '(?\C-g ?\C-g ?\C-g)))
+         ;; Tell `read-from-minibuffer' not to read from stdin when in
+         ;; batch mode.
+         (executing-kbd-macro t))
+     ,@body))
+
 (defun ert-run-idle-timers ()
   "Run all idle timers (from `timer-idle-list')."
   (dolist (timer (copy-sequence timer-idle-list))
diff --git a/test/lisp/emacs-lisp/find-func-tests.el b/test/lisp/emacs-lisp/find-func-tests.el
new file mode 100644
index 00000000000..f505e78566e
--- /dev/null
+++ b/test/lisp/emacs-lisp/find-func-tests.el
@@ -0,0 +1,45 @@
+;;; find-func-tests.el --- Unit tests for find-func.el  -*- lexical-binding: t; -*-
+
+;; Copyright (C) 2020 Free Software Foundation, Inc.
+
+;; Author: Stefan Monnier <monnier@iro.umontreal.ca>
+;; Keywords:
+
+;; 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.
+
+;; You should have received a copy of the GNU General Public License
+;; along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+;;; Commentary:
+
+;;
+
+;;; Code:
+
+(require 'ert-x)                        ;For `ert-run-keys'.
+
+(ert-deftest find-func-tests--library-completion () ;bug#43393
+  ;; FIXME: How can we make this work in batch (see also
+  ;; `mule-cmds--test-universal-coding-system-argument')?
+  ;; (skip-unless (not noninteractive))
+  ;; Check that `partial-completion' works when completing library names.
+  (should (equal "org/org"
+                 (ert-simulate-keys
+                     (kbd "o / o r g TAB RET")
+                   (read-library-name))))
+  ;; Check that absolute file names also work.
+  (should (equal (expand-file-name "nxml/" data-directory)
+                 (ert-simulate-keys
+                     (concat data-directory (kbd "n x / TAB RET"))
+                   (read-library-name)))))
+
+(provide 'find-func-tests)
+;;; find-func-tests.el ends here
diff --git a/test/lisp/international/mule-tests.el b/test/lisp/international/mule-tests.el
index 5f8e653d7c2..9520d9d8633 100644
--- a/test/lisp/international/mule-tests.el
+++ b/test/lisp/international/mule-tests.el
@@ -23,6 +23,8 @@
 
 ;;; Code:
 
+(require 'ert-x)                        ;For `ert-run-keys'.
+
 (ert-deftest find-auto-coding--bug27391 ()
   "Check that Bug#27391 is fixed."
   (with-temp-buffer
@@ -41,12 +43,11 @@
   (should (not (multibyte-string-p (encode-coding-char ?a 'utf-8)))))
 
 (ert-deftest mule-cmds--test-universal-coding-system-argument ()
-  (skip-unless (not noninteractive))
   (should (equal "ccccccccccccccccab"
-                 (let ((enable-recursive-minibuffers t)
-                       (unread-command-events
-                        (append (kbd "C-x RET c u t f - 8 RET C-u C-u c a b RET") nil)))
-                   (read-string "prompt:")))))
+                 (let ((enable-recursive-minibuffers t))
+                   (ert-simulate-keys
+                       (kbd "C-x RET c u t f - 8 RET C-u C-u c a b RET")
+                     (read-string "prompt:"))))))
 
 (ert-deftest mule-utf-7 ()
   ;; utf-7 and utf-7-imap are not ASCII-compatible.