+1

Works with Twitter as well.

I wanted to find my (real-world) friend here, and add him to my friends list.
However I am new to this GUI and find it quite confusing.
I think I've clicked all promissing icons, but still havent found something like a "users search".
BTW. I was dissapointed that the "Feedback" icon does not let me leave my feedback for the product, but rathers shows some notifications:P
In a moment of enlightment I've visited my profile, where I found the "following" section, which unfortunatly shows no Call To Action, just a sad unclickable sentence "Youu have not started to follow any users yet." which does not provide any solution to resolve this pressing issue;)
My "advice": whenever you find yourself designing/implementing a "there is no things to show here" text, think about users who see this text and wonder how to change the state of affairs. You could easily fix this with a better text like : "You are not following anyone, to start following visit this place, or do this action", or just embed the needed tool inline ("Type in username you are searching for here").

I see no way to handle both 29th and 28th test case.

I think that solutions which use an array internally to store functions, and modify this array on add(), miss the point of reusability.
In my opinion reusability is achieved when add() returns a new instance, without altering the previous one, so both can be used.
I'd suggest to add a test which tests for reusability, something like:
var smallNumbersOnly = new Lazy().add(filterNumbers).add(filterRange, 2, 7);
var maxNumber = smallNumbersOnly.add(max);
smallNumbersOnly.invoke([1,8,"6",4,7]) == [4,7]
maxNumber.invoke([1,8,"6",4,7]) == 7

I believe it would be benefitial to distinguish between 'expression' and 'statement' in the specification.
I think the current spec is simply wrong when it says that each Input will be an expression, while the grammar defines expression as something which does not contain = operator.
I think the intention was to say that Input will be a statement, which can be an assignment or an expression.