diff --git a/test/lisp/shadowfile-tests.el b/test/lisp/shadowfile-tests.el
index 200fb4c58c..e1a260c336 100644
--- a/test/lisp/shadowfile-tests.el
+++ b/test/lisp/shadowfile-tests.el
@@ -19,6 +19,18 @@
 
 ;;; Commentary:
 
+;; Some of the tests require access to a remote host files.  Since
+;; this could be problematic, a mock-up connection method "mock" is
+;; used.  Emulating a remote connection, it simply calls "sh -i".
+;; Tramp's file name handlers still run, so this test is sufficient
+;; except for connection establishing.
+
+;; If you want to test a real Tramp connection, set
+;; $REMOTE_TEMPORARY_FILE_DIRECTORY to a suitable value in order to
+;; overwrite the default value.  If you want to skip tests accessing a
+;; remote host, set this environment variable to "/dev/null" or
+;; whatever is appropriate on your system.
+
 ;; A whole test run can be performed calling the command `shadowfile-test-all'.
 
 ;;; Code:
@@ -27,28 +39,28 @@
 (require 'shadowfile)
 (require 'tramp)
 
-;; There is no default value on w32 systems, which could work out of the box.
 (defconst shadow-test-remote-temporary-file-directory
   (cond
    ((getenv "REMOTE_TEMPORARY_FILE_DIRECTORY"))
-   ((eq system-type 'windows-nt) null-device)
-   (t (add-to-list
-       'tramp-methods
-       '("mock"
-	 (tramp-login-program        "sh")
-	 (tramp-login-args           (("-i")))
-	 (tramp-remote-shell         "/bin/sh")
-	 (tramp-remote-shell-args    ("-c"))
-	 (tramp-connection-timeout   10)))
-      (add-to-list
-       'tramp-default-host-alist
-       `("\\`mock\\'" nil ,(system-name)))
-      ;; Emacs' Makefile sets $HOME to a nonexistent value.  Needed in
-      ;; batch mode only, therefore.  It cannot be
-      ;; `temporary-directory', because the tests with "~" would fail.
-      (unless (and (null noninteractive) (file-directory-p "~/"))
-        (setenv "HOME" invocation-directory))
-      (format "/mock::%s" temporary-file-directory)))
+   ((executable-find "sh")
+    (add-to-list
+     'tramp-methods
+     `("mock"
+       (tramp-login-program        ,(executable-find "sh"))
+       (tramp-login-args           (("-i")))
+       (tramp-remote-shell         ,(executable-find "sh"))
+       (tramp-remote-shell-args    ("-c"))
+       (tramp-connection-timeout   10)))
+    (add-to-list
+     'tramp-default-host-alist
+     `("\\`mock\\'" nil ,(system-name)))
+    ;; Emacs' Makefile sets $HOME to a nonexistent value.  Needed in
+    ;; batch mode only, therefore.  It cannot be
+    ;; `temporary-directory', because the tests with "~" would fail.
+    (unless (and (null noninteractive) (file-directory-p "~/"))
+      (setenv "HOME" invocation-directory))
+    (format "/mock::%s" temporary-file-directory))
+   (t null-device))
   "Temporary directory for Tramp tests.")
 
 (defconst shadow-test-info-file