Question

I have a program that will be running several system commands. The simplest way I know how to do this is with the ` ` notation. I’d like to build tests for these tools without it actually having to run those system commands on the system.

Is there a way I can mock the response from the system?

Answer 1

If your code runs a lot of external commands you should create a simple wrapper and mock that:

def wants_to_run_external_command(command_runner)
  command_runner.run('echo "hello world"')
end

and test it like this:

it 'echos "hello world"' do
  command_runner = double()
  command_runner.should_receive(:run).with('echo "hello world"')
  subject.wants_to_run_external_command(command_runner)
end

If you want to be neater you initialize your object with the command runner instance so you don’t have to pass it to the method, of course.