A formal test plan is a document that provides and records important information about a test project, for example:
project and quality assumptions
project background information
resources
schedule & timeline
entry and exit criteria
test milestones
tests to be performed
use cases and/or test cases
For a range of reasons -- both good and bad -- many software and web development projects don't budget enough time for complete and comprehensive testing. A quality test team must be able to test a product or system quickly and constructively in order to provide some value to the project.
Identify High-Level Functions First
High-level functions are those functions that are most important to the central purpose(s) of the site or application. A test plan would typically provide a breakdown of an application's functional groups as defined by the developers; for example, the functional groups of a commerce web site might be defined as shopping cart application, address book, registration/user information, order submission, search, and online customer service chat. If this site's purpose is to sell goods online, then you have a quick-and-dirty prioritization of:
