`tr 'A-Z' 'a-z'` will only convert non-accented characters. Switching to `[:upper:]` and `[:lower:]` adds support for accents. See https://github.com/koalaman/shellcheck/wiki/SC2018 Additionally, printf's character splitting does not support accented characters, so output isn't as expected. Using bash's variable expansion syntax instead will correctly get the full accented character.
Testing with Bats
To execute the unit tests, please run the run script:
# If you are in the `test` directory:
./run
# If you are in the root `.bash_it` directory:
test/run
The run script will automatically install Bats if it is not already present, and will then run all tests found under the test directory, including subdirectories.