Here's the duo strand about inclusion of articles.
Nitram includes this rule:
Do no use the article in structures with adverbs of place using the preposition "in"
Also, here are some really good examples ..
"in pizzeria, ingelateria, in macelleria, insalumeria, in profumeria, inperiferia etc. ... in banca, in piscina, in biblioteca,in discoteca, in palestra, inufficio, in chiesa, in campagna,in montagna, in edicola, incentro, in periferia, in vacanza etc."
.. taken from this link
It looks like the preposition "in" goes before buildings and/or places, xyphax. I went to your second link and took the test. I missed six questions but I got four questions correct! Is the Benvenuti link taken from a textbook or is it a course? No one said a foreign language was easy! heee! heee! Thanks!
There are involved different culinary traditions: in Italy there aren't bakeries! If I'm not wrong at the Anglo-Saxon bakery you can buy cakes, puddings, muffins, meatpie.. sweet and salt things, anything "baked". Traditionally you can't buy creams or jellies in a bakery, do you? In Italy, "panetteria" is where you buy bread (a lot of type of bread) and nothing else (maybe some biscuits, of course nothing with meat); "pasticceria" is where you buy only sweets: cakes, creams, tiramisù, biscuits, fingerfoods, candies etc. (nothing with salt); "gastronomia" is where you buy all the rest "baked" (lasagna, roast beef, etc.)
I think that Lodoviko is correct about this distinction. "Pastry shop" is a more appropriate translation than 'bakery."
For certain types of shops, etc., in Italian, they use "in pasticceria" for in the bakery. another example is "in macelleria" in the butcher shop. I don't have any grammar books with me, however, somewhere on the 'net one should be able to find a listing.