So I am not sure if this should go in the shell forum or in the beginners. It is my first time posting on these forums.

I have a directory, main_dir lets say, with multiple sub directories (one_dir through onehundred_dir for example) and in each sub directory there is a test.txt. How would one rename all the text.txt files after thier respective subdir name.
so from:

main_dir/one_dir/test.text
main_dir/two_dir/test.text
...
...

to:
main_dir/one_dir/one_dir.text
main_dir/two_dir/two_dir.text
...
...
Any assistance would be really helpful. And if you could point me to a resource to learn these kind of things on my own without just reading all the man pages I would appreciate that as well.
Thanks,
robotsbite