Dockertest.test.yml documentation?

I’m looking for documentation on *.test.yml files.

For example: I tried the following:

sut:
  build: .
  command: cat /etc/issue
  command: pwd
  command: whoami 
  command: ls -l

But when I looked at the build logs it appeared the only command to execute was the last one (ls -l). Is there a page with examples and documentation for creating the *.test.yml files? Is it one command per file?

Edit: Testing shows that it appears to be one command per file. Still looking for documentation.