Added test to determine num of elements with class

[anrddh]

Closes #1762

Apologies for the oversight.

[bugron]

@awesomeaniruddh not sure why there are two single quotes at the end of "assert($(\"p.red-text\").length === 2, 'Give each of your <code>p</code> elements the <code>red-text</code> class.'')",? This causes an error.
Also I want to discuss thes.

"Give the elements with the red-text class the font-size of 16px." seems there is an extra the (or two), but I'm not sure at this point.

[anrddh]

^ Fixed the thes. Seems like me text editor did that. Let me fix it. Phew.

[anrddh]

Yep, done.

[bugron]

@awesomeaniruddh Excellent, verified and merged, thanks for the PR!