All Hipot Testers on the market will have a High Voltage terminal and a Return Terminal. The test is performed by applying a voltage, usually greater than 1000V to the line conductors of the item under test (usually Live and Neutral).
The High Voltage terminal connected to the line conductors and the Return Terminal, usually connected to the Chassis of the product, or the Earth Conductor. The test voltage is applied and the current flowing across the conductors is measured, providing this level of current is low enough not to pose a hazard, the test will complete and the item under test will be deemed safe.
To save time it is normal that the live and neutral conductors are strapped together during this test, rather than testing each one individually against the ground.