Abstract: A system for well testing enables well test fluids to be injected into an existing well, either to a reservoir or into an existing subsea production stream and onto a processing facility, thus eliminating the requirement for flaring. The system has fluids passed through a well test package for measurement and any necessary treatment before being returned via a second fluid conduit, connection, and ancillaries and into a receiving reservoir or existing subsea production stream. The fluids may be produced to surface via a BOP and marine riser (or alternative fluid conduit and connection) or produced and passed through a subsea well test package for measurement without being produced to the surface.