The gst-validate-launcher uses a set of test cases and media files, the gstreamer
team provides gst-integration-testsuites [1] but you could provide your own. 

To get gst-integration-testsuites uses git-annex to get media:

$ git clone git://anongit.freedesktop.org/gstreamer/gst-integration-testsuites
$ cd gst-integration-testsuites
$ git checkout 1.12 
$ git annex get

The gst-integration-testsuites needs to be pre-populated into the rootfs inside
/gst-validate folder,

$ mkdir /ROOTFS_PATH/gst-validate
$ cp -rf gst-integration-testsuites /ROOTFS_PATH/gst-validate

[1] https://cgit.freedesktop.org/gstreamer/gst-integration-testsuites