Villages. Can someone legitimatly expand a village by building more houses for villagers (Testificates) to breed and fill? Would these houses have any conditions to be met beyond a roof and a door?
Yes, a village can be expanded.
The Village House
A building is a village house if it has a wooden door, an "inside" and an "outside". The "inside" needs a light level of less than 15 and should not have a direct view of the sky, while the outside needs a light level of 15 and a direct view of the sky. The "inside" is the side which has more "roof" blocks than the other side of the door, with the "roof" blocks being within a five block range from the door. A house does not have any requirements other than those three. An example of the smallest house is something like this:
"The dirt blocks the light from reaching the space below it, and so counts as a roof block. There is one "inside" space, covered by a roof block, on the right side of the image and zero on the left. Since one is more than zero, there are more covered spaces on one side of the door than there are on the other, and so the game counts this as a house."
Breeding of Villagers
Villagers will try to breed to keep the population above 35% of the total amount of houses. A villager must become "willing" in order to breed. If you want to make villagers willing, you can add a farm, or give the villager either 3 bread items, 12 carrots, 12 potatoes or 12 beetroots. Villagers with too much food will throw their food to other villagers, in order to make them willing too. You can also make them willing by trading with them. When trading a new item with them for the first time, they will become willing. They also have a 1/5 chance to become willing once you trade with them. If they become willing after you trade with them, green "sparkly" particles will appear above them. These particles are called
Warning in Regard to Expansion
Note that a Zombie Siege can occur if a player is in the village and if the number of houses is above 10 or the number of villagers is above 20.
Yes, this is entirely possible. I keep meaning to do it myself, but haven't gotten around to it. Villagers will breed until there are .35*[number of doors] villagers. To be defined as a house, the building must have at least one block with no opaque blocks blocking its view of the sky.
In Minecraft 1.8, the Willingness mechanic was introduced in order to make it more difficult to rapidly breed villagers. A villager will always become willing to breed the first time a new offer is traded, and has a 20% chance of becoming willing from each subsequent trade of that offer.
Alternatively, a villager can become willing by having 3 bread, 12 carrots, 12 potatoes, or 12 beetroots in a single stack in their inventory. Upon becoming willing, the villager will consume the required food from their inventory. If a villager has more than the required amount of food (generally from farming) they will throw the excess food to other villagers. You can also throw food to villagers yourself to get them to the required food level.
As of 1.8, villager mechanics are changed, to where you can still build houses the same way as before (a door and a block at least 5 blocks behind it, you can put extra doors in between) but the villagers will not breed until the are "willing." You must trade with a villager until green particles appear, and then do it again for a nearby villager.
So, the answer to your question is yes. It just takes a lot of resources and time.
Villagers will only breed when they are "willing". This can be achieved through trading and by ensuring they have lots of food (either 3 bread, 12 carrots, 12 potatoes, or 12 beetroots in one stack in their inventory). After mating, they will no longer be willing, and must be made willing again. All this is trumped by the door rule - villagers will mate until the number of adult villagers equals or is more than 35% of the number of doors in the village. "Villager generators" still work in 1.10.2 though, what I normally do is surround a farm (garden,field) with doors and then place a block above each door on the "inside" of the farm. I have a village with 12 naturally occurring doors as well as three of my generators and my village population currently includes 12 adults, four children and an iron golem.