ApTest's VSU test suite verifies the compliance of systems to SPEC1170 - The Open Group's Single UNIX standard. VSU verifies over 450 new interfaces added to The Open Group's XPG4 specifications by SPEC1170.

VSU is employed by The Open Group in its conformance branding program for licensing the UNIX trademark.

VSU features include:

• The industry's first tests for the popular sockets and STREAMS networking interfaces. These interfaces are key to the development of portable client server applications.
• Extensive tests for development environments, ensuring a common application can be installed and built across systems bearing the UNIX trademark.
• Tests for many interfaces originating in common UNIX variants: System V, Berkeley UNIX and OSF/1, providing a unified application environment across all these Operating Systems.
• Tests for the widely used CURSES terminal user interface package.
• Implementation under the Test Environment Toolkit (TET), facilitating easy integration with existing test suites.
• Automated installation and configuration tools.
• Sophisticated test report generators that facilitate analyzing problems and achieving compliance.

VSU can be licensed through ApTest for use in Open Group branding or for other purposes.