What is a Delivery?
A Delivery is a published Test, and as such is immutable. Comparable to a physically published text (such as a pdf file) and its source (e.g. Word) document, consequent changes in the test do not impact a delivery. An author would need to create a new delivery, i.e. re-publish the test, for the changes made to a particular test to take effect for the Test-takers assigned to the new delivery.
In practice, a delivery is the assembly of all the information required to assign and send out tests to selected test-takers. This includes such information as the test which is to be delivered, the group of test-takers to receive the test, and the circumstances (in particular the time frame) in which the test may be taken.
Deliveries effectively define the life cycle of an Item session (i.e. the time between test-takers starting an item and finishing it). This cycle begins when the test-taker becomes eligible for a test delivery, a condition that is set during the actual authoring of the delivery. In simple terms, the cycle continues through the test-taker's completing of the tests selected, and ends when test Results for all Interactions are determined. In some instances, more than one attempt to interact may be allowed, and the delivery life cycle continues until no remaining attempts are permitted. The cycle finishes when the results are recorded; these may or may not be displayed to the test-taker, but they are made available to at least the test administrator after the life cycle is complete.