Feature #20901: Run a shell linter on bash scripts and add unit tests
Add initial unit tests for shell scripts
After examining the different option for unit tests in shell seems that BATS may be a good start.
It was chosen for its simple syntax.
bats-mock may be an useful adds-on since alias may not play well w/ BATS.
shellspec is a close second for its BDD syntax and the coverage reports.
shunit2 is also worth considering if different ones are compared
The test directory will be /test/bats (from the project source)
The first candidates will be the functions in singularity_lib.sh and the singularity wrapper.