A test article is a version of space craft or related vehicle or equipement, built as a platform to perform testing. Test articles are built to the same specifications to replicate conditions and behaviors of flight ready versions. Test article version are also built without the certification and quality control steps taken with the versions intended for flight. Test articles are more complete than a boilerplate.
Test articles can sometimes be upgraded to flight ready status. Of the 136 Space Shuttle external fuel tanks produced, one was retained as a test article. The contractor producing the tanks commented that that tank could be refurbished for flight use if necessary.
The static test article for the Dream Chaser lifting-body

Lifting body

A lifting body is a fixed-wing aircraft configuration in which the body itself produces lift. In contrast to a flying wing, which is a wing with minimal or no conventional fuselage, a lifting body can be thought of as a fuselage with little or no conventional wing...

 spaceplane

Spaceplane

A spaceplane is a vehicle that operates as an aircraft in Earth's atmosphere, as well as a spacecraft when it is in space. It combines features of an aircraft and a spacecraft, which can be thought of as an aircraft that can endure and maneuver in the vacuum of space or likewise a spacecraft that...

 "will become the atmospheric flight test vehicle in 2012 for drop tests."

Test articles are often displayed in museums because of their accuracy. Museums may refurbish test articles to match more modern configurations. This was completed on the Hubble Space Telescope

Hubble Space Telescope

The Hubble Space Telescope is a space telescope that was carried into orbit by a Space Shuttle in 1990 and remains in operation. A 2.4 meter aperture telescope in low Earth orbit, Hubble's four main instruments observe in the near ultraviolet, visible, and near infrared...

 Structural Dynamic Test Vehicle on display at the National Air and Space Museum

National Air and Space Museum

The National Air and Space Museum of the Smithsonian Institution holds the largest collection of historic aircraft and spacecraft in the world. It was established in 1976. Located in Washington, D.C., United States, it is a center for research into the history and science of aviation and...

where this 1976 version of the vehicle was removed from display and upgraded in 1996 by the Smithsonian, Lockheed, and NASA to incorporate changes made on the on-mission version of the Hubble Space Telescope over several servicing missions.