A test apparatus for torsional testing of a wind turbine blade, comprising: a test stand for rigidly supporting a root end of the wind turbine blade; a load frame for mounting on the wind turbine blade at a testing position along the length of the wind turbine blade; and a pair of actuators connected to the load frame for exerting a force thereon characterised in that: the test stand supports the blade in an orientation with the blade edgewise direction arranged substantially vertically; the load frame comprises an outer frame and a profiled insert held within the outer frame, the profiled insert defining a profiled aperture substantially corresponding to the profile of the wind turbine blade at the testing position such that, in use, the profiled insert substantially encloses and is in direct contact with the outer surface of substantially the entire profile of the wind turbine blade; and the pair of actuators are mounted on a support frame to provide a fixed mounting point fixed relative to the ground and connected to the outer frame of the load frame at opposite sides of the blade longitudinal axis each acting in substantially vertical opposed directions for twisting the wind turbine blade about its longitudinal axis via the load frame. a test stand for rigidly supporting a root end of the wind turbine blade; a load frame for mounting on the wind turbine blade at a testing position along the length of the wind turbine blade; and a pair of actuators connected to the load frame for exerting a force thereon characterised in that: the test stand supports the blade in an orientation with the blade edgewise direction arranged substantially vertically; the load frame comprises an outer frame and a profiled insert held within the outer frame, the profiled insert defining a profiled aperture substantially corresponding to the profile of the wind turbine blade at the testing position such that, in use, the profiled insert substantially encloses and is in direct contact with the outer surface of substantially the entire profile of the wind turbine blade; and the pair of actuators are mounted on a support frame to provide a fixed mounting point fixed relative to the ground and connected to the outer frame of the load frame at opposite sides of the blade longitudinal axis each acting in substantially vertical opposed directions for twisting the wind turbine blade about its longitudinal axis via the load frame. the test stand supports the blade in an orientation with the blade edgewise direction arranged substantially vertically; the load frame comprises an outer frame and a profiled insert held within the outer frame, the profiled insert defining a profiled aperture substantially corresponding to the profile of the wind turbine blade at the testing position such that, in use, the profiled insert substantially encloses and is in direct contact with the outer surface of substantially the entire profile of the wind turbine blade; and the pair of actuators are mounted on a support frame to provide a fixed mounting point fixed relative to the ground and connected to the outer frame of the load frame at opposite sides of the blade longitudinal axis each acting in substantially vertical opposed directions for twisting the wind turbine blade about its longitudinal axis via the load frame.