Add a TESTING.md document describing how to run the unit test suite

Reviewers: #kwin

Subscribers: kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D16777

TESTING.md

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+# Testing in KWin
+KWin provides a unit and integration test suit for X11 and Wayland. The source code for the tests can be found in the subdirectory autotests. The test suite should be run prior to any merge to KWin.
+
+# Dependencies
+The following additional software needs to be installed for running the test suite:
+
+* Xvfb
+* Xephyr
+* glxgears
+* DMZ-white cursor theme
+* breeze window decoration
+
+# Preparing a run of the test suite
+Please load the kernel module "vgem". This is required to provide a virtual OpenGL device.
+
+    sudo modprobe vgem
+
+Furthermore the user executing the test suite must be able to read and write to the dri device created by vgem.
+
+# Running the test suite
+The test suite can be run from the build directory. Best is to do:
+
+    cd path/to/build/directory
+    xvfb-run ctest
+
+# Running individual tests
+All tests executables are created in the directory "bin" in the build directory. Each test can be executed by just starting it from within the test directory. To prevent side effects with the running session it is recommended to start a dedicated dbus session:
+
+    cd path/to/build/directory/bin
+    dbus-run-session ./testFoo
+
+For tests relying on X11 one should also either start a dedicated Xvfb and export DISPLAY or use xvfb-run as described above.