Apologies if this is a dumb question. I glanced at the linked document and it is not obvious to me if this is for testing bash or for testing bash scripts.
Neither. It’s called that because it’s using a dialect/DSL of bash.
It’s a general unit test tool, but working in bash orients Bats towards testing of scripted/automated infrastructure. I’ve used it for tests of Chef/Puppet configuration and found Bats a good fit. Seems odd to find it used as the test framework for a data management tool but clearly it floats their boat.