The two rows of holes (labelled #3) are test points used during the manufacture of this USB memory key.

Testpoints on a printed circuit board (labelled E34, E35, E36, …) next to teardrop vias

A test point is a location within an electronic circuit that is used to either monitor the state of the circuitry or to inject test signals. Test points have three primary uses:

• During development they are used to analyze hardware behavior. This allows characterization of circuit boards (e.g. power consumption, bus bandwidth), validation of the design and evaluation of component selection. For hardware with software components, test points are used to monitor bus signal, provide engineering interfaces and to force behaviors. Not all development test points are incorporated in production devices.
• During manufacturing they are used to verify that a newly assembled device is working correctly. Any equipment that fails this testing is either discarded or sent to a rework station to attempt to repair the manufacturing defects.
• After sale of the device to a customer, test points may be used at a later time to repair the device if it malfunctions, or if the device needs to be re-calibrated after having components replaced.

Test points can be labeled and may include pins for attachment of alligator clips or may have complete connectors for test clips.

Modern miniature surface-mount electronics often simply have a row of unlabelled, tinned solder pads. The device is placed into a test fixture that holds the device securely, and a special surface-contact connector plate is pressed down onto the solder pads to connect them all as a group.