It may be hard to tell unless you ask somebody who contributes to those projects but the benefit of being open source is that you can inspect the tree and commit log. You may be able to use this to see which order tests come with respect to the actual code.
As for agile, there may be some practices that are difficult to achieve with largely distributed teams such as pair programming and sprint meetings. The nature of contributions could mean faster iteration/integration cycles.
The main thing is many contribute out of enjoyment. Some may not enjoy working to a formal methodology but rather a set of general guidelines that give room for autonomy. If the code's good and correct, does it matter how it came to be?