Add empty spec for UrlReferenceable.
Forgot the 'do'.
Add skeleton for UrlReferenceable.
Add stubs for the expected methods.
Add contexts.
Add parent mocking.
Add no-parent-empty-string test.
Make test pass..
Add parent_url no parent test.
Make it pass.
Expect #parent_url to call #parent.
Forgot to call #parent_url in tests
Make it pass.
Expect #parent_url to call #url on the parent
Specify no arguments are given.
Forgot to stub :parent and :url.
Forgot :parent was already stubbed...
Remove .once, as we don't need to specify this
Make it pass
Specify that #parent_url should return the URL