Add test cases for generated nodes

[kazuhitoyokoi]

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)

Proposed changes

I added test cases for the following nodes created by node-red-nodegen command.

• function node (created from JavaScript code in sample/lower-case.js)
• swagger node (created from swagger definition in http://petstore.swagger.io/v2/swagger.json)

Checklist

• I have read the contribution guidelines
• For non-bugfix PRs, I have discussed this change on the mailing list/slack team.
• I have run grunt to verify the unit tests pass
• I have added suitable unit tests to cover the new/changed functionality

[coveralls]

Coverage decreased (-40.3%) to 32.893% when pulling 381c06b on kazuhitoyokoi:master into a96d9ed on node-red:master.

[coveralls]

Coverage decreased (-40.3%) to 32.893% when pulling 381c06b on kazuhitoyokoi:master into a96d9ed on node-red:master.