From: Brian Candler <b.candler@...>
Date: 2010-05-12T19:19:52+09:00
Subject: Re: Unit Test of method calling system() - how?

Martin Hansen wrote:
> test "Options.parse with empty argv and existing wiki file don't raise" 
> do
>   opt_parser = Options.new
>   assert_nothing_raised() { opt_parser.parse([],"/foo/bar.rb") }
> end

    if full
      system("print_wiki --data_in #{@wiki_path} --help")
    else
      system("print_wiki --data_in #{@wiki_path}")
    end

    raise "Failed printing wiki: #{@wiki_path}" if $?

AFAICS this will always raise, since $? will never be nil. I think you 
want:

    raise ... unless $?.success?

> However, the original problem remains - I really want to test the 
> following:
> 
> test "Options.parse with empty argv and existing wiki output short 
> usage" do
>   opt_parser = Options.new
>   assert("<exp short>" == opt_parser.parse([],"/foo/bar.rb"))
> end
> 
> test "Options.parse with --help in argv and existing wiki output long 
> usage" do
>   opt_parser = Options.new
>   assert("<exp long>" == opt_parser.parse(["--help"],"/foo/bar.rb"))
> end

In that case you would need to collect the output from print_wiki, for 
example using the IO.popen code I showed before.

> I am actually not interested in the invocation of print_wiki, since this 
> Perl script is tested - so never mind about testing the 
> print_usage_and_exit -> good enuf for government work... But I am 
> interested in testing the print_usage_full? and print_usage_short? 
> methods. So how to do that?

Well, that's what mocking is for. You say you don't actually want to run 
print_usage_and_exit, so I think you want to check that it *would* have 
been run, with the correct arguments to do what you want.

  opt_parser = Options.new
  opt_parser.expects(:print_usage_and_exit).with()
  assert_nothing_raised { opt_parser.parse([], "/foo/bar.rb") }

At the end of your test method, if :print_usage_and_exit wasn't called, 
or was called with different arguments, you'll get an error raised by 
the mocking framework. The awkward thing is that print_usage_and_exit 
might actually be called multiple times, so it may be worth changing the 
call to

  if print_usage_full?
    print_usage_and_exit(true)
    return  # not reached except in testing
  end

As for $0: this tends to be dangerous anyway (it is subject to 
truncation under various conditions). __FILE__ is safer, giving the 
location of the current source file, if that's usable.

But otherwise I would be inclined to move this logic out into the code 
which calls the option parser: i.e.

  def parse(argv, wiki_path)
    @wiki_path = wiki_path
    ...
  end

and then in your main bin file:

  opt_parser.parse(ARGV, ENV["BP_DIR"] + "/bp_usage/" + 
File.basename($0, ".rb") + ".wiki"))

Just a suggestion.
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