Content Update Option I'm using Drupal 7. I made a couple of content types and taxonomies. Is there any way to select multiple content in the same content type and modify their fields together?

For instance, I have account type with the fields: account number, test case, ...

I want to set multiple account contents' test case to the same value. 

Note: the test case is just a field with a selection of test case names, sry about the confusion
If you're coding up test cases -- not really. You could build the nodes programatically with some test account numbers, etc. But, you'd have to do that by hand. There are alot of tutorials for SimpleTest and creating nodes in drupal.

If you need a GUI to alter many node fields at once, take a look at Views Bulk Operations (VBO).