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docs/layout_tests_linux.md

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+# Running layout tests on Linux
+
+  1. Build `blink_tests` (see LinuxBuildInstructions)
+  1. Checkout the layout tests
+    * If you have an entry in your .gclient file that includes "LayoutTests", you may need to comment it out and sync.
+    * You can run a subset of the tests by passing in a path relative to `src/third_party/WebKit/LayoutTests/`.  For example, `run_layout_tests.py fast` will only run the tests under `src/third_party/WebKit/LayoutTests/fast/`.
+  1. When the tests finish, any unexpected results should be displayed.
+
+See [Running WebKit Layout Tests](http://dev.chromium.org/developers/testing/webkit-layout-tests) for full documentation about set up and available options.
+
+## Pixel Tests
+
+The pixel test results were generated on Ubuntu 10.4 (Lucid).  If you're running a newer version of Ubuntu, you will get some pixel test failures due to changes in freetype or fonts.  In this case, you can create a Lucid 64 chroot using `build/install-chroot.sh` to compile and run tests.
+
+## Fonts
+
+Make sure you have all the necessary fonts installed.
+```
+sudo apt-get install apache2 wdiff php5-cgi ttf-indic-fonts \
+   msttcorefonts ttf-dejavu-core ttf-kochi-gothic ttf-kochi-mincho \
+   ttf-thai-tlwg
+```
+
+You can also just run `build/install-build-deps.sh` again.
+
+## Plugins
+
+If `fast/dom/object-plugin-hides-properties.html` and `plugins/embed-attributes-style.html` are failing, try uninstalling `totem-mozilla` from your system:
+```
+sudo apt-get remove totem-mozilla
+```
+
+## Running layout tests under valgrind on Linux
+
+As above, but use `tools/valgrind/chrome_tests.sh -t webkit` instead.  e.g.
+```
+sh tools/valgrind/chrome_tests.sh -t webkit LayoutTests/fast/
+```
+This defaults to using --debug.  Read the script for more details.
+
+If you're trying to reproduce a run from the valgrind buildbot, look for the --run\_chunk=XX:YY
+line in the bot's log.  You can rerun exactly as the bot did with the commands
+```
+cd ~/chromium/src
+echo XX >  valgrind_layout_chunk.txt
+sh tools/valgrind/chrome_tests.sh -t layout -n YY
+```
+That will run the XXth chunk of YY layout tests.
+
+## Configuration tips
+  * Use an optimized content\_shell when rebaselining or running a lot of tests.  ([bug 8475](http://code.google.com/p/chromium/issues/detail?id=8475) is about how the debug output differs from the optimized output.)  `ninja -C out/Release content_shell`
+  * Make sure you have wdiff installed: `sudo apt-get install wdiff` to get prettier diff output
+  * Some pixel tests may fail due to processor-specific rounding errors. Build using a chroot jail with Lucid 64-bit user space to be sure that your system matches the checked in baselines.  You can use `build/install-chroot.sh` to set up a Lucid 64 chroot. Learn more about [UsingALinuxChroot](UsingALinuxChroot.md).
+## Getting a layout test into a debugger
+
+There are two ways:
+  1. Run content\_shell directly rather than using run\_layout\_tests.py. You will need to pass some options:
+    * `--no-timeout` to give you plenty of time to debug
+    * the fully qualified path of the layout test (rather than relative to `WebKit/LayoutTests`).
+  1. Or, run as normal but with the `--additional-drt-flag=--renderer-startup-dialog  --additional-drt-flag=--no-timeout --time-out-ms=86400000` flags. The first one makes content\_shell bring up a dialog before running, which then would let you attach to the process via `gdb -p PID_OF_DUMPRENDERTREE`. The others help avoid the test shell and DumpRenderTree timeouts during the debug session.
+
+## Using an embedded X server
+
+If you try to use your computer while the tests are running, you may get annoyed as windows are opened and closed automatically.  To get around this, you can create a separate X server for running the tests.
+
+  1. Install Xephyr (`sudo apt-get install xserver-xephyr`)
+  1. Start Xephyr as display 4: `Xephyr :4 -screen 1024x768x24`
+  1. Run the layout tests in the Xephyr: `DISPLAY=:4 run_layout_tests.py`
+
+Xephyr supports debugging repainting.  See the [Xephyr README](http://cgit.freedesktop.org/xorg/xserver/tree/hw/kdrive/ephyr/README) for details.  In brief:
+  1. `XEPHYR_PAUSE=$((500*1000)) Xephyr ...etc...  # 500 ms repaint flash`
+  1. `kill -USR1 $(pidof Xephyr)`
+
+If you don't want to see anything at all, you can use Xvfb (should already be installed).
+  1. Start Xvfb as display 4: `Xvfb :4 -screen 0 1024x768x24`
+  1. Run the layout tests in the Xvfb: `DISPLAY=:4 run_layout_tests.py`
+
+## Tiling Window managers
+
+The layout tests want to run with the window at a particular size down to the pixel level.  This means if your window manager resizes the window it'll cause test failures.  This is another good reason to use an embedded X server.
+
+### xmonad
+In your `.xmonad/xmonad.hs`, change your config to include a manageHook along these lines:
+```
+test_shell_manage = className =? "Test_shell" --> doFloat
+main = xmonad $
+  defaultConfig
+    { manageHook = test_shell_manage <+> manageHook defaultConfig
+    ...
+```