The River Test is a chalk stream in Hampshire in the south of England. It rises at Ashe near Basingstoke and flows southwards for 40 miles (64 km) to Southampton Water. Settlements on the Test include the towns of Stockbridge and Romsey. The river's valley gives its name to the local government district of Test Valley. Below the village of Longparish, the river is broadly followed by the Test Way, a long-distance footpath.

Chalk streams are rivers that rise from springs in landscapes with chalk bedrock. Since chalk is permeable, water percolates easily through the ground to the water table and chalk streams therefore receive little surface runoff. As a result, the water in the streams contains little organic matter and sediment and is generally very clear.