While Cyndaquil is not part of the Test Your Mettle Event in 1-Star Raid in Pokémon GO.

Cyndaquil is a Fire-type pocket monster that serves as the base form for Quilava and Typhlosion in Pokémon GO. This single elemental characteristic enables echidna to be resistant to Fire-, Bug-, Steel-, Grass-, Ice-, and Fairy-type Moves. However, Trainers can easily defeat this Raid Boss by using a Pokémon team with Ground-, Water-, or Rock-type Movesets. Although Cyndaquil is only a 1-Star Raid, novice Trainers are encouraged to bring at least one friend along just in case things go south. For example, Mamoswine possesses Moves that can deal effective damage to Cyndaquil, but it can also take more damage due to its Ice element. Therefore, it's also important to consider the elemental type of one's lineup before facing a Raid Boss.

Related: Pokémon GO: Girafarig Raid Guide (Best Counters & Weaknesses)

Thanks to "best" counters in Pokémon GO, they should not fret, as any combatant with Ground-, Water-, or Rock-type Movesets will suffice against the fiery echidna.

How To Counter Cyndaquil In A Pokémon GO Raid

Best Water Counters For Cyndaquil

Best Ground & Rock Counters For Cyndaquil

Source: Pokebattler