Test a bash pipeline

There is a bash script which runs a Python code that is basically a pipeline with a couple of steps. The pipeline creates some files and I want to test for their presence verify their data format is correct, so that the pipeline, after each step, is verified to have run that concrete step correctly (something like STEP 1: [PASS], which means that the test for that step has passed). How and where to write these tests? Is there appropriate library that can be used? Thanks.