Just install the texlive-xetex package:
texlive-xetex
sudo apt-get install texlive-xetex
Rails LTS provides security patches for old versions of Ruby on Rails (2.3, 3.2, 4.2 and 5.2)
Running integration tests without texlive-xetex will produce an error during xelatex execution:
xelatex
RTeX::Document::ExecutableNotFoundError