gst-launch is not a good tool to show that your element is finished. Applications such as Rhythmbox and Totem (for GNOME) or AmaroK (for KDE) are. gst-launch will not test various things such as proper clean-up on reset, event handling, querying and so on.
From gstreamer web page:
https://gstreamer.freedesktop.org/documentation/plugin-development/appendix/checklist-element.html