Add test for responseURL

[berniegp]

Description

Adds a unit test showing how to set the responseURL attribute of a request response.

This PR contains:

• [ ] bugfix
• [ ] feature
• [ ] refactor
• [x] documentation
• [ ] other

Are tests included?

• [x] yes (bugfixes and features will not be merged without tests)
• [ ] no

Breaking Changes?

• [ ] yes (breaking changes are only considered with a good reason)
• [x] no

Related issue numbers: #50