Using QuickTest you can define and store your user-defined functions either in a function library (saved as a .qfl file by default) or directly in an action within a test. A function library is a Visual Basic script containing VBscript functions subroutines modules and so forth. You can also use QuickTest to modify and debug any existing function libraries (such as .vbs or .txt files).

When you store a function in a function library and associate the function library with a test the test can call the public functions in that function library. Functions that are stored in an associated function library can be accessed from the Step Generator (for tests and function libraries) and the Operation column in the Keyword View as well as being entered manually in the Expert View.

When you store a function in a test action it can be called only from within that action—the function cannot be called from any other action or test. This is useful if you do not want the function to be available outside of a specific action.

You can also define private functions and store them in a function library. Private functions are functions that can be called only by other functions within the same function library. This is useful if you to reuse segments of code in your public functions.