Test CLI with parameters

I assume this is very newbie stuff but I'm learning Ruby by doing, and I'm doing a small CLI tool that receives a couple of parameters in order to do its stuff properly. This is my current workflow:

I want to test (using Minitest) all the possible flows:

• Exits with 0 and help message is shown if ARGV.count != 2
• Exists with 1 if first param is not correct
• Exists with 1 if second param is not correct
• Exists with 1 if both params are not correct
• Exists with 0 and does stuff if all params are correct

Now, if I run tests the only thing I see is the help output as there is no parameter being passed.

So, a couple of questions:

• How can I pass arguments to the main program in tests?
• How can I test the output? (I'm using puts)

Thanks!