On 2016-07-07 11:15, Eli Zaretskii wrote:
> They also risk introducing bugs, and we don't really have a test
> suite for the display engine to be sure we didn't screw up anything.

Richard recently suggested giving Emacs the ability to take a screenshot of itself. Could we imagine using this to run regression tests of the display engine?

I already use a similar process in one of my packages: the idea is to script Emacs using a simple DSL (see https://github.com/cpitclaudel/company-coq/blob/master/etc/rebuild-screenshots.el#L419 for an example, and https://github.com/cpitclaudel/company-coq/blob/master/img/match-function.gif for the output), and record a screenshot after each command; then, I use these images to generate the README page on https://github.com/cpitclaudel/company-coq/. Since these images are checked in, any time a change has visible consequences I see it immediately, and I can use ImageMagick to get a visual diff.

Of course, it could be hard to get screeenshots to looks exactly the same for everyone. Instead, we could have a makefile target that builds a large collection of these screenshots, and another one that rebuilds it and compares against a previously generated one.

Clément.