--- /dev/null
+;;; 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