Fix recently uncovered 'make check' failures

For discussion, see the following thread:
https://lists.gnu.org/r/emacs-devel/2021-01/msg01111.html

* test/lisp/autorevert-tests.el
(auto-revert-test07-auto-revert-several-buffers):
* test/lisp/emacs-lisp/seq-tests.el (test-seq-do-indexed)
(test-seq-random-elt-take-all): Fix errors from using add-to-list on
lexical variables.
* test/lisp/emacs-lisp/cl-lib-tests.el
(cl-lib-defstruct-record): Expect test to succeed when byte-compiled
following change of 2021-01-23 'Fix missing file&line info in
"Unknown defun property" warnings'.
(cl-lib-tests--dummy-function): Remove; no longer needed.
(old-struct): Silence byte-compiler warning about unused lexical
variable.

test/lisp/emacs-lisp/cl-lib-tests.el

@@ -543,15 +543,7 @@
                            (apply (lambda (x) (+ x 1)) (list 8)))))
                  '(5 (6 5) (6 6) 9))))
 
-(defun cl-lib-tests--dummy-function ()
-  ;; Dummy function to see if the file is compiled.
-  t)
-
 (ert-deftest cl-lib-defstruct-record ()
-  ;; This test fails when compiled, see Bug#24402/27718.
-  :expected-result (if (byte-code-function-p
-                        (symbol-function 'cl-lib-tests--dummy-function))
-                       :failed :passed)
   (cl-defstruct foo x)
   (let ((x (make-foo :x 42)))
     (should (recordp x))
@@ -566,6 +558,7 @@
     (should (eq (type-of x) 'vector))
 
     (cl-old-struct-compat-mode 1)
+    (defvar cl-struct-foo)
     (let ((cl-struct-foo (cl--struct-get-class 'foo)))
       (setf (symbol-function 'cl-struct-foo) :quick-object-witness-check)
       (should (eq (type-of x) 'foo))

test/lisp/emacs-lisp/seq-tests.el

@@ -29,6 +29,9 @@
 (require 'ert)
 (require 'seq)
 
+(eval-when-compile
+  (require 'cl-lib))
+
 (defmacro with-test-sequences (spec &rest body)
   "Successively bind VAR to a list, vector, and string built from SEQ.
 Evaluate BODY for each created sequence.
@@ -108,16 +111,12 @@ Evaluate BODY for each created sequence.
                  '((a 0) (b 1) (c 2) (d 3)))))
 
 (ert-deftest test-seq-do-indexed ()
-  (let ((result nil))
-    (seq-do-indexed (lambda (elt i)
-                      (add-to-list 'result (list elt i)))
-                    nil)
-    (should (equal result nil)))
+  (let (result)
+    (seq-do-indexed (lambda (elt i) (push (list elt i) result)) ())
+    (should-not result))
   (with-test-sequences (seq '(4 5 6))
-    (let ((result nil))
-      (seq-do-indexed (lambda (elt i)
-                        (add-to-list 'result (list elt i)))
-                      seq)
+    (let (result)
+      (seq-do-indexed (lambda (elt i) (push (list elt i) result)) seq)
       (should (equal (seq-elt result 0) '(6 2)))
       (should (equal (seq-elt result 1) '(5 1)))
       (should (equal (seq-elt result 2) '(4 0))))))
@@ -410,12 +409,10 @@ Evaluate BODY for each created sequence.
 
 (ert-deftest test-seq-random-elt-take-all ()
   (let ((seq '(a b c d e))
-        (elts '()))
-    (should (= 0 (length elts)))
+        elts)
     (dotimes (_ 1000)
       (let ((random-elt (seq-random-elt seq)))
-        (add-to-list 'elts
-                     random-elt)))
+        (cl-pushnew random-elt elts)))
     (should (= 5 (length elts)))))
 
 (ert-deftest test-seq-random-elt-signal-on-empty ()