How to test OptionParser with Rspec - RSpec options are stored in ARGV array during testing

Question

I am learning ruby and trying to write a unit test with rspec for the following method:

def get()
    options = {}
    OptionParser.new do |opt|
      opt.banner = 'Usage: validate-gitlab-ci [options]'
                    
      opt.on('-f', '--yaml YAML-PATH', 'Path to .gitlab-ci.yml') { |o| options[:yamlFile] = o }
      opt.on('-l', '--base-url GitLab url', 'GitLab API url') { |o| options[:baseUrl] = o + API_PATH }
      opt.on('-t', '--timeout[TIMEOUT]', Integer, 'Api timeout in seconds') { |o| options[:timeout] = o || 10 }
      opt.on('-v', '--version', 'Program version') { |o| options[:version] = o }
    end.parse!
                
    validateUrl!(options[:baseUrl])
    validateYamlFile!(options[:yamlFile])

    @baseUrl = options[:baseUrl]
    @pathToYamlFile = options[:yamlFile]
end

The code for my unit test so far is:

RSpec.describe Gitlab::Lint::Client::Args do
    describe "#get" do
        context "when arguments are valid" do
            it "sets baseUrl and pathToYamlFile" do
                io = StringIO.new
                io.puts "glab-lint --base-url=https://example.com --yaml=valid.ym\n"
                io.rewind

                $stdin = io
                args = Gitlab::Lint::Client::Args.new
                args.get()
                expect(args.baseUrl).to.eq("https://example.com")
            end
        end
    end
end

I am trying to mock STDIN for OptionParser. However, upon executing the test the following error is displayed:

 OptionParser::InvalidOption:
       invalid option: --pattern

This is raised by the end.parse! line in the get() method

Has anyone managed to test OptionsParser with stdin mocked?

Update

I think what is happening is that some RSpec options, e.g. --pattern?? are being captured in STDIN and passed to script??? Or .... RSpec is consuming the stdin options??

Reading this post seems to suggest that the desired functionality is not possible with RSpec....if this is indeed true then I will migrate over to using alternative test frameworks in future for CLI projects that use ARGV. There is a workaround suggested here but that suggests using environment variables for capturing commmand line arguments. In this case that would require further refactoring of the software under test, purely to suit the capabilities of the RSpec test framework!!

If I add a puts statement to display the contents of ARGV in the test script it confirms this is the case, with this output:

--pattern
spec/**{,/*/**}/*_spec.rb
[--base-url=https://gitlab.com --yaml=valid.ym]

So.....as a complete newbie to RSpec.....my options are:

1. Update the signature of the get method to accept an args array:

def get(args)
    options = {}
    OptionParser.new do |opt|
    ...
    end.parse!(args)
end

This delays the issue with testing the code that reads from ARGV further up the call hierarchy

2. Modify ARGV shifting the first two arguments out of the array and then after the test has completed restore ARGV to original state. Looks like something similar has already been tried here without success.

3. Some other configuration that I am not aware of as a newbie to RSpec

4. Investigate alternative options, e.g. minitest, that maybe do not modify the ARGV array??

Further information regarding options 3 and 4 appreciated....

Answer 1

You can use RSpec to mock STDIN. For example:

STDIN.should_receive(:read).and_return("glab-lint --base-url=https://example.com --yaml=valid.yml")

Alternatively, you can invoke your actual command line program using backticks or system, and assert on the response.