Google has presumably stopped recruiting from the foobar coding challenges.

While the general method of randomly selecting potential candidates for the challenge is still the same, i.e. scanning through their google searches and for particular keywords, there are certain methods using which one can get a foobar invitation.
Note that, as Google has stopped recruiting, this method can still be used to try out some good programming challenges.
To get an invitation, open a new tab and search for “Arraylist Java”.
Now open duplicate tabs and search for the same thing using the search url generated by first tab.

After around 20 tabs, you will receive a notification on your search screen saying “You seem to speak our language! Up for a challenge?”
et voila!

This method works 100%

EDIT:— As this method is old, the folks at Google might have already detected the flaw in their algorithm and have disabled this method.

So now I can't be sure of its certainty