Check the display successfully starts before returning

[mithro]

(Fix this TODO)

We use the xdpyinfo tool in our own code to check if a X server is working.

Code something like this would work;

start_time = time.time()
while time.time() - start_time < START_TIMEOUT:
    # We don't explicitly set the display, as we want to check the
    # environment value.
    exit_code = subprocess.call(['xdpyinfo'])
    if exit_code == 0:
        logging.info('Successfully started Xvfb with display "%s".', display)
        return
    logging.warn('xdpyinfo check failed with exit code %s while starting Xvfb on "%s".', exit_code, display)
    time.sleep(0.1)
logging.fatal('Failed to start Xvfb on display "%s" (xdpyinfo check failed).', display)

[mithro]

(I'm opening this issue as I hope to send you a pull request with a fix soon.)

[The-Compiler]

xdpyinfo won't necessarily be installed, though.

[mithro]

We can probably try a bunch of different tools (xeyes was a previous test tool :-)

[ponty]

Other X11 tools:

https://packages.debian.org/jessie/x11-apps

 - atobm, bitmap, and bmtoa, tools for manipulating bitmap images;
 - ico, a demo program animating polyhedrons;
 - oclock and xclock, graphical clocks;
 - rendercheck, a program to test render extension implementations;
 - transset, a tool to set opacity property on a window;
 - xbiff, a tool which tells you when you have new email;
 - xcalc, a scientific calculator desktop accessory;
 - xclipboard, a tool to manage cut-and-pasted text selections;
 - xconsole, which monitors system console messages;
 - xcursorgen, a tool for creating X cursor files from PNGs;
 - xditview, a viewer for ditroff output;
 - xedit, a simple text editor for X;
 - xeyes, a demo program in which a pair of eyes track the pointer;
 - xgc, a graphics demo;
 - xload, a monitor for the system load average;
 - xlogo, a demo program that displays the X logo;
 - xmag, which magnifies parts of the X screen;
 - xman, a manual page browser;
 - xmore, a text pager;
 - xwd, a utility for taking window dumps ("screenshots") of the X session;
 - xwud, a viewer for window dumps created by xwd;
 - Xmark, x11perf, and x11perfcomp, tools for benchmarking graphical
   operations under the X Window System;

https://packages.debian.org/jessie/x11-utils

 - appres, editres, listres and viewres, which query the X resource database;
 - luit, a filter that can be run between an arbitrary application and a
   UTF-8 terminal emulator;
 - xdpyinfo, a display information utility for X;
 - xdriinfo, query configuration information of DRI drivers;
 - xev, an X event displayer;
 - xfd, a tool that displays all the glyphs in a given X font;
 - xfontsel, a tool for browsing and selecting X fonts;
 - xkill, a tool for terminating misbehaving X clients;
 - xlsatoms, which lists interned atoms defined on an X server;
 - xlsclients, which lists client applications running on an X display;
 - xlsfonts, a server font list displayer;
 - xmessage, a tool to display message or dialog boxes;
 - xprop, a property displayer for X;
 - xvinfo, an Xv extension information utility for X;
 - xwininfo, a window information utility for X;

[ponty]

Check with xdpyinfo is implemented.