Makefile for Ruby tests

I know about Rake::TestTask.

But, how would I write a Makefile to achive similar functionality?

I want to be able to run all my Ruby tests by running:

make test

It'd also be nice to have a way to run one test file, e.g.:

TEST=just_one_file.rb make test

I use MiniTest.

I want this because I like Make, and I want to start using it more.

I figured seeing this example would help me.

I also don't understand what rake test does under the scenes, so seeing the Makefile might help me understand how tests run.