Their first three studio albums, The Legacy (1987), The New Order (1988) and Practice What You Preach (1989), cemented Testament's reputation as one of the most successful thrash metal bands, with the latter becoming their first to enter the Top 100 on the Billboard 200 chart.

[13] Clemente and Skolnick had both left Testament by the end of 1992, and within the next decade, the band had endured many personnel changes that included guitarists Glen Alvelais, James Murphy, Steve Smyth and "Metal" Mike Chlasciak, bassists Derrick Ramirez (who was originally in Legacy as a guitarist) and Di Giorgio, and drummers Paul Bostaph, John Tempesta, Jon Dette, Chris Kontos, Gene Hoglan, Dave Lombardo, Steve Jacobs and Jon Allen.

In 2001, at around the same time Billy was diagnosed with germ cell seminoma, Testament reunited with Souza, Skolnick and Tempesta for the album of re-recorded material First Strike Still Deadly.

Testament's popularity was revived with the albums The Formation of Damnation (2008), Dark Roots of Earth (2012), Brotherhood of the Snake (2016) and Titans of Creation (2020), all entering the Top 100 on the Billboard 200,[13] and they have continued to tour consistently.

They eventually hired drummer Louie Clemente, vocalist Steve "Zetro" Souza and bassist Greg Christian, and began playing club shows with bands such as Exodus, Slayer, Anthrax, Lȧȧz Rockit and Death Angel, among others.

Thanks to this, and the regular rotation of their first-ever music video "Over the Wall" on MTV's Headbangers Ball,[17] the band quickly managed to increase their exposure by heading out on successful North American and European tours with Anthrax, who were supporting their Among the Living album.

The album was a minor success, peaking at number 136 on the Billboard 200,[13] but managed to sell over 250,000 copies on the strength of the airplay of "Trial by Fire" and the cover version of Aerosmith's "Nobody's Fault" (through radio and television), as well as relentless touring schedules.

[16] They also made a number of festival appearances during the summer of 1988, such as Metalfest in Milwaukee, Aardschokdag in The Netherlands, and replaced Megadeth on some dates of the European Monsters of Rock tour, also featuring Iron Maiden, Kiss, David Lee Roth, Great White and Anthrax.

[21][22] Practice What You Preach was a commercial breakthrough for Testament, reaching at number 77 on the Billboard 200,[13] and it was accompanied by three singles – the title track, "The Ballad" and "Greenhouse Effect" – that received significant airplay from AOR radio stations and MTV's Headbangers Ball, further helping raise the band's profile.

[17][18][23][24] Testament toured for nearly a year behind Practice What You Preach, performing with numerous bands such as Overkill, Annihilator, Wrathchild America, Mortal Sin, Xentrix, Nuclear Assault, Savatage, Flotsam and Jetsam, Mordred, Dark Angel and a then-lesser known Primus.

[33] Drummer Louie Clemente acknowledged this musical change in a 1992 interview with Deseret News, explaining, "The Ritual is slower and geared toward the old style of metal while The Legacy was pure thrash.

Testament toured for over a year in support of Low, playing with numerous acts such as Machine Head, downset., Korn, Forbidden, Kreator, At the Gates, Moonspell, Crowbar, Suffocation and Gorefest.

Tempesta left Testament shortly before the release of Low to join White Zombie, being replaced by Jon Dette for the following tour, though the latter would leave the band in 1995.

Hoglan's loyalty to Strapping Young Lad and his desire to not remain a member of Testament actually came to realization during a published interview the band conducted with Metal Maniacs magazine.

The rhythm section on The Gathering was highly respected, consisting of metal fretless bassist Steve Di Giorgio (formerly of Death and Sadus) and original Slayer drummer Dave Lombardo.

The show was headlined by a Legacy reunion, featuring Steve Souza on vocals, and former guitarist Alex Skolnick, who had not played with the band since 1992, and bassist Greg Christian.

It featured the lineup of Billy, Peterson, Di Giorgio, the return of Souza on vocals (for the album's last two tracks), Skolnick on guitar, and John Tempesta on drums.

The band announced that they had recruited guitarist Glen Drover (ex-Megadeth and King Diamond) to fill in on their upcoming Mexican tour dates with Judas Priest, due to Alex Skolnick's prior commitment to the Trans-Siberian Orchestra.

[50] On March 25, 2009, Testament played a special one-off show at the O2 Islington Academy in London, where they performed their first two albums (The Legacy and The New Order) back-to-back, with British thrash band Sylosis in support.

In an interview with Metalheadz, Peterson stated that there were about four songs written and that "there's other guys in the band who like to play the more rock melodic style but the next one is gonna be a bit heavier.

"[50] In a January 2011 interview during the 70000 Tons of Metal cruise, Billy revealed that Testament had been working on six new songs, with four or five "maybe left to write," and would begin recording their new album by early March.

[67][68][69] When asked in an April 2015 interview about Testament's plans to begin recording their twelfth album, Peterson said that his "main goal" was to "get home [from tour] in June, finish it up and get in the studio by September.

[71] Slovenian bassist Tilen Hudrap (Pestilence, Vicious Rumors, Paradox and Thraw) and Bay Area drummer Alex Bent (Arkaik, Dragonlord, Hatriot, Decrepit Birth and Battlecross) filled in for Di Giorgio and Hoglan respectively at the prestigious Canadian open-air festival Heavy Montréal in August 2015, which was attended by more than 70,000 spectators.

[78] Along with Anthrax, Lamb of God, Behemoth and Napalm Death, Testament opened for Slayer on their final North American tour, which took place throughout the spring and summer of 2018.

[106][107] On some dates of the latter tour, Phil Demmel (formerly of Vio-lence and Machine Head) stepped in for guitarist Alex Skolnick, as the latter had sat out in order to tend to a family emergency.

[108] In a May 2020 interview with Exodus and former Legacy frontman Steve "Zetro" Souza on his "Toxic Vault" video channel, Billy was asked if he was going to write another Testament album during the COVID-19 pandemic.

[111] In a March 2021 interview on Alive & Streaming, an internet podcast hosted by Death Angel guitarist Ted Aguilar, Billy confirmed that Peterson has been writing new material for what could result in the next Testament album.

[112] On January 21, 2022, the band and longtime drummer Gene Hoglan announced on their respective social media accounts that he had once again left Testament to pursue "an exciting new chapter of [his] career and free agency, with all that it will entail.

[143][144][145][146][147][148][149] Numerous hard rock and heavy metal acts, such as Aerosmith, AC/DC, Angel Witch, Black Sabbath, Boston, Deep Purple, Def Leppard, Dio, Exodus, Iron Maiden, Judas Priest, Kiss, Led Zeppelin, Mercyful Fate, Metallica, the Michael Schenker Group, Montrose, Ozzy Osbourne (particularly the Randy Rhoads-era), Raven, Samson, Saxon, Scorpions, Slayer, the Sweet, Thin Lizzy, UFO (particularly the Michael Schenker-era), Van Halen, Venom and Watchtower, have been cited as an influence or inspiration to Testament's music.

[137][150][151] The band's other musical influences or inspirations include The Beatles, as well as guitarists/vocalists Jeff Beck, Chuck Berry, Jimi Hendrix, Yngwie Malmsteen, Frank Marino, Mahogany Rush, Pat Travers and Johnny Winter.