Add failing tests for blank SOURCE_REPO environment variable
user
```ruby
require 'test_helper'

class ConfiguratorTest < ActiveSupport::TestCase

  [
    {env_value: nil, expected: 'https://github.com/octobox/octobox'},
    {env_value: '', expected: 'https://github.com/octobox/octobox'},
    {env_value: ' ', expected: 'https://github.com/octobox/octobox'},
    {env_value: 'https://github.com/foo/bar', expected: 'https://github.com/foo/bar'}
  ].each do |t|
    env_value_string = t[:env_value].nil? ? 'nil' : "'#{t[:env_value].to_s}'"
    test "When ENV['SOURCE_REPO'] is #{env_value_string}, config.source_repo is '#{t[:expected]}'" do
      stub_env_var('SOURCE_REPO', t[:env_value])
      assert_equal t[:expected], Octobox.config.source_repo
    end
  end

end```
assistant