ert-x: Move window selection logic to its own macro

* lisp/emacs-lisp/ert-x.el (ert-with-buffer-selected): New macro to
temporarily display a buffer in a selected window and evaluate a body.
(ert-with-test-buffer-selected): Use the new macro.
* test/lisp/whitespace-tests.el
(ert-test-with-buffer-selected/current)
(ert-test-with-buffer-selected/selected)
(ert-test-with-buffer-selected/nil-buffer)
(ert-test-with-buffer-selected/modification-hooks)
(ert-test-with-buffer-selected/read-only)
(ert-test-with-buffer-selected/return-value): Add tests.
(Bug#60189)

2 files changed, 55 insertions, 10 deletions

diff --git a/lisp/emacs-lisp/ert-x.el b/lisp/emacs-lisp/ert-x.el
index 5f1c5c26acd..0614313809c 100644
--- a/lisp/emacs-lisp/ert-x.el
+++ b/lisp/emacs-lisp/ert-x.el
@@ -102,25 +102,36 @@ the name of the test and the result of NAME-FORM."
            (indent 1))
   `(ert--call-with-test-buffer ,name-form (lambda () ,@body)))
 
-(cl-defmacro ert-with-test-buffer-selected ((&key name)
-                                            &body body)
-  "Create a test buffer, switch to it, and run BODY.
+(cl-defmacro ert-with-buffer-selected (buffer-or-name &body body)
+  "Display a buffer in a temporary selected window and run BODY.
+
+If BUFFER-OR-NAME is nil, the current buffer is used.
 
-This extends `ert-with-test-buffer' by displaying the test
-buffer (whose name is derived from NAME) in a temporary window.
-The temporary window becomes the `selected-window' before BODY is
-evaluated.  The modification hooks `before-change-functions' and
+The buffer is made the current buffer, and the temporary window
+becomes the `selected-window', before BODY is evaluated.  The
+modification hooks `before-change-functions' and
 `after-change-functions' are not inhibited during the evaluation
 of BODY, which makes it easier to use `execute-kbd-macro' to
 simulate user interaction.  The window configuration is restored
 before returning, even if BODY exits nonlocally.  The return
 value is the last form in BODY."
-  (declare (debug ((":name" form) body)) (indent 1))
-  `(ert-with-test-buffer (:name ,name)
-     (save-window-excursion
+  (declare (debug (form body)) (indent 1))
+  `(save-window-excursion
+     (with-current-buffer (or ,buffer-or-name (current-buffer))
        (with-selected-window (display-buffer (current-buffer))
          ,@body))))
 
+(cl-defmacro ert-with-test-buffer-selected ((&key name) &body body)
+  "Create a test buffer, switch to it, and run BODY.
+
+This combines `ert-with-test-buffer' and
+`ert-with-buffer-selected'.  The return value is the last form in
+BODY."
+  (declare (debug ((":name" form) body)) (indent 1))
+  `(ert-with-test-buffer (:name ,name)
+     (ert-with-buffer-selected (current-buffer)
+       ,@body)))
+
 ;;;###autoload
 (defun ert-kill-all-test-buffers ()
   "Kill all test buffers that are still live."
diff --git a/test/lisp/emacs-lisp/ert-x-tests.el b/test/lisp/emacs-lisp/ert-x-tests.el
index f14d54cd9f7..1cfd218592a 100644
--- a/test/lisp/emacs-lisp/ert-x-tests.el
+++ b/test/lisp/emacs-lisp/ert-x-tests.el
@@ -82,6 +82,40 @@
         (should-not (buffer-live-p buffer-1))
         (should (buffer-live-p buffer-2))))))
 
+(ert-deftest ert-test-with-buffer-selected/current ()
+  (let ((origbuf (current-buffer)))
+    (ert-with-test-buffer ()
+      (let ((buf (current-buffer)))
+        (should (not (eq buf origbuf)))
+        (with-current-buffer origbuf
+          (ert-with-buffer-selected buf
+            (should (eq (current-buffer) buf))))))))
+
+(ert-deftest ert-test-with-buffer-selected/selected ()
+  (ert-with-test-buffer ()
+    (ert-with-buffer-selected (current-buffer)
+      (should (eq (window-buffer) (current-buffer))))))
+
+(ert-deftest ert-test-with-buffer-selected/nil-buffer ()
+  (ert-with-test-buffer ()
+    (let ((buf (current-buffer)))
+      (ert-with-buffer-selected nil
+        (should (eq (window-buffer) buf))))))
+
+(ert-deftest ert-test-with-buffer-selected/modification-hooks ()
+  (ert-with-test-buffer ()
+    (ert-with-buffer-selected (current-buffer)
+      (should (null inhibit-modification-hooks)))))
+
+(ert-deftest ert-test-with-buffer-selected/read-only ()
+  (ert-with-test-buffer ()
+    (ert-with-buffer-selected (current-buffer)
+      (should (null inhibit-read-only))
+      (should (null buffer-read-only)))))
+
+(ert-deftest ert-test-with-buffer-selected/return-value ()
+  (should (equal (ert-with-buffer-selected nil "foo") "foo")))
+
 (ert-deftest ert-test-with-test-buffer-selected/selected ()
   (ert-with-test-buffer-selected ()
     (should (eq (window-buffer) (current-buffer)))))