I'm going to try to answer my own question.
code here.
The second most important sentence in tompave's answer is
Normally it would be user_path
for singular routes (show, update, delete) and users_path
for the plural ones (index, create). Here, however, users_path
must be used for the singular routes, and Rails will fallback to use users_index_path
for index
and create
.
The person who coded up the Rspec test seems to have known using the plural form "Articles" would generate the articles_index_path method rather than article_path.
And thus my confusion has been addressed.
I wish I could thank tompave directly