The cover of the single was taken from the 1968 Olympics Black Power Salute. The song's lyrics notably make reference to George Orwell's novel 1984 through use of "The Party" slogan "Who controls the past (now), controls the future. Who controls the present (now), controls the past." The song is a playable track on Rock Band 2.

A song titled "Testify" was performed at the KROQ Almost Acoustic X-Mas, 12.12.1993. The song is completely unrelated to the Battle of Los Angeles track except for the title. Although the song was played only this once and disappeared, some of the lyrics were used for "Down Rodeo" and the final version of "People of the Sun."

"Testify" made its live debut on January 28, 1999, at the Continental Arena in East Rutherford, NJ. While the instrumental part was identical to the final version, the lyrics were completely different.

Rage Against the Machine opened most of their concerts in their reunion tour with "Testify".

The song, like many Rage Against the Machine songs, is notable for Tom Morello's unorthodox use of his guitar to create unusual sounds. Morello plays the sweeping sound in the song's intro and verse using a mixture of effects and techniques. First, the DigiTech Whammy pedal is set to harmonize a minor 7th above the note being played, and the delay pedal is set to a short, slap-back setting that almost sounds like reverb. Morello creates the sound by simply picking the open low D string and using a wah-wah pedal to slowly shift back & forth between the bass and treble frequencies. For the song's solo, Morello removes the lead from the jack of his guitar and taps it against the bridge, while manipulating his wah-wah and DigiTech Whammy pedals, creating a squealing noise. Morello sometimes uses this technique to improvise on songs live.

...
Wikipedia