Move adding test files to "beforeEach()"

All the tests in the "Renaming files" section added the test files,
although those calling "doRename()" added them by setting a path for the
file too. However, the path is ignored in the other tests, so adding the
files can be unified and moved to "beforeEach()".

This would be needed, for example, to show the details view for a file
before calling "doRename()".

Signed-off-by: Daniel Calviño Sánchez <danxuliu@gmail.com>