An ultrasonic testing technique in which the transducer is not parallel to the test surface is called?

Angle beam testing is the correct answer because it specifically involves the use of a transducer that is positioned at an angle to the test surface, allowing for the generation of ultrasonic waves that can reflect off flaws or discontinuities within the material. This technique is particularly useful for detecting defects in welds or materials where the initial beam path would not be effective due to the orientation of the potential flaws.

In contrast, direct beam testing refers to the use of a transducer that is positioned perpendicular to the testing surface, which typically aims to assess the material straight through rather than at an angle. Surface wave testing involves the use of surface waves generated along the surface of the material rather than through it. Finally, through-transmission testing uses two transducers placed on opposite sides of the material, with one sending ultrasonic waves and the other receiving them, which does not involve angling the transducer in relation to the test surface. Thus, angle beam testing is the only method among the options listed that involves a non-parallel orientation to the surface being tested.