You can use wildcards with the :edit command. So,
:e **/test/Suite.java
will open test/Suite.java no matter where it is in the current directory hierarchy. This works with tab-completion so you can use [tab] to expand the wildcards before opening the file. See also the wildmode option for a way to browse through all possible extensions instead.
Another trick is to use
:r! find . -type f
to load a list of all files in the current directory into a buffer. Then you can use all the usual vim text manipulation tools to navigate/sort/trim the list, and CTRL+W gf to open the file under the cursor in a new pane.