If you want to view all tests changes, you can do that from Site Administration as follows:
From Site Administration (must have Site Admin permissions) goto Site Projects tab

*Select the project in question and click the + sign to expand the view of the tables

*Run the following query from the Audit_Log table:

Replace the default query SELECT * FROM AUDIT_LOG with

SELECT * FROM AUDIT_LOG where au_entity_type = 'TEST' or au_entity_type = 'DESSTEPS'

The list of items returned will include all tests and test steps with the date, and the user who made the changes.

Hope this helps!