This is an excerpt from Complete Conditioning for Soccer by Ryan Alexander.
Yo-Yo Endurance Test (Beep Test)
The Yo-Yo endurance test is a multistage, continuous assessment. Unlike the recovery tests, there is no break between shuttles. Traditionally this progressively intense conditioning assessment has been deemed an assessment of a player's aerobic power.
Mark two lines 65 feet, 7.4 inches (20 m) apart (figure 2.2). Acquire an audio recording for this test, which guides players through the different stages until exhaustion.
Figure 2.2 Yo-Yo endurance test (beep test) setup.
Players begin on one line designated by cones. When signaled by the audio recording, players run across the designated space to the opposite line before the next beep. At the sound of the next beep, players return to the starting line, keeping pace with the recording's signals. The time between beeps decreases, forcing players to increase their running speed. A player who is unable to cover the distance within the time allotted by the audio recording receives a warning. The assessment is finished if the player is unable to cover the distance prior to the signal a second time. The player's score is recorded as the last successful shuttle that they were able to complete.
The scoring for the Yo-Yo endurance test is similar to the Yo-Yo intermittent recovery test in that you can track shuttles completed, then multiply that number by 20 meters to get the total distance covered. Please be aware there are multiple versions of the audio recording for the Yo-Yo endurance test. Be consistent with the version used so that the results are comparable.