Add tests for scrolling

* test/manual/scroll-tests.el: New tests for scroll-margin behavior.

test/manual/scroll-tests.el

@@ -0,0 +1,130 @@
+;;; scroll-tests.el -- tests for scrolling -*- lexical-binding: t -*-
+
+;; Copyright (C) 2017 Free Software Foundation, Inc.
+
+;; This file is part of GNU Emacs.
+
+;; 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 <http://www.gnu.org/licenses/>.
+
+;;; Commentary:
+
+;; These are mostly automated ert tests, but they don't work in batch
+;; mode which is why they are under test/manual.
+
+;;; Code:
+
+(require 'ert)
+(eval-when-compile (require 'cl-lib))
+
+(defun scroll-tests-up-and-down (margin &optional effective-margin)
+  (unless effective-margin
+    (setq effective-margin margin))
+  (erase-buffer)
+  (insert (mapconcat #'number-to-string
+                     (number-sequence 1 200) "\n"))
+  (goto-char 1)
+  (sit-for 0)
+  (let ((scroll-margin margin)
+        (wstart (window-start)))
+    ;; Stopping before `scroll-margin' so we shouldn't have
+    ;; scrolled.
+    (let ((current-prefix-arg (- (window-text-height) 1 effective-margin)))
+      (call-interactively 'next-line))
+    (sit-for 0)
+    (should (= wstart (window-start)))
+    ;; Passing `scroll-margin' should trigger scrolling.
+    (call-interactively 'next-line)
+    (sit-for 0)
+    (should (/= wstart (window-start)))
+    ;; Scroll back to top.
+    (let ((current-prefix-arg (window-start)))
+      (call-interactively 'scroll-down-command))
+    (sit-for 0)
+    (should (= 1 (window-start)))))
+
+(defmacro scroll-tests-with-buffer-window (&rest body)
+  (declare (debug t))
+  `(with-temp-buffer
+     (with-selected-window (display-buffer (current-buffer))
+       ,@body)))
+
+(ert-deftest scroll-tests-scroll-margin-0 ()
+  (skip-unless (not noninteractive))
+  (scroll-tests-with-buffer-window
+   (scroll-tests-up-and-down 0)))
+
+(ert-deftest scroll-tests-scroll-margin-negative ()
+  "A negative `scroll-margin' should be the same as 0."
+  (skip-unless (not noninteractive))
+  (scroll-tests-with-buffer-window
+   (scroll-tests-up-and-down -10 0)))
+
+(ert-deftest scroll-tests-scroll-margin-max ()
+  (skip-unless (not noninteractive))
+  (scroll-tests-with-buffer-window
+   (let ((max-margin (/ (window-text-height) 4)))
+     (scroll-tests-up-and-down max-margin))))
+
+(ert-deftest scroll-tests-scroll-margin-over-max ()
+  "A `scroll-margin' more than max should be the same as max."
+  (skip-unless (not noninteractive))
+  (scroll-tests-with-buffer-window
+   (set-window-text-height nil 7)
+   (let ((max-margin (/ (window-text-height) 4)))
+     (scroll-tests-up-and-down (+ max-margin 1) max-margin)
+     (scroll-tests-up-and-down (+ max-margin 2) max-margin))))
+
+(defun scroll-tests--point-in-middle-of-window-p ()
+  (= (count-lines (window-start) (window-point))
+     (/ (1- (window-text-height)) 2)))
+
+(cl-defun scroll-tests--scroll-margin-whole-window (&key with-line-spacing)
+  "Test `maximum-scroll-margin' at 0.5.
+With a high `scroll-margin', this should keep cursor in the
+middle of the window."
+  (let  ((maximum-scroll-margin 0.5)
+         (scroll-margin 100))
+    (scroll-tests-with-buffer-window
+     (setq-local line-spacing with-line-spacing)
+     ;; Choose an odd number, so there is one line in the middle.
+     (set-window-text-height nil 7)
+     ;; `set-window-text-height' doesn't count `line-spacing'.
+     (when with-line-spacing
+       (window-resize nil (* line-spacing 7) nil nil 'pixels))
+     (erase-buffer)
+     (insert (mapconcat #'number-to-string
+                        (number-sequence 1 200) "\n"))
+     (goto-char 1)
+     (sit-for 0)
+     (call-interactively 'scroll-up-command)
+     (sit-for 0)
+     (should (scroll-tests--point-in-middle-of-window-p))
+     (call-interactively 'scroll-up-command)
+     (sit-for 0)
+     (should (scroll-tests--point-in-middle-of-window-p))
+     (call-interactively 'scroll-down-command)
+     (sit-for 0)
+     (should (scroll-tests--point-in-middle-of-window-p)))))
+
+(ert-deftest scroll-tests-scroll-margin-whole-window ()
+  (skip-unless (not noninteractive))
+  (scroll-tests--scroll-margin-whole-window))
+
+(ert-deftest scroll-tests-scroll-margin-whole-window-line-spacing ()
+  ;; `line-spacing' has no effect on tty displays.
+  (skip-unless (display-graphic-p))
+  (scroll-tests--scroll-margin-whole-window :with-line-spacing 3))
+
+
+;;; scroll-tests.el ends here