X3m.System.Test.Scheduler.start_link

You're seeing just the function start_link, go back to X3m.System.Test.Scheduler module for more information.
Link to this function

start_link(state \\ %{})

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Specs

start_link(state :: any()) :: GenServer.on_start()

Spawns Scheduler with given state. That one is provided in all callbacks as last parameter and can be used to provide Repo or any other detail needed.

When new Scheduler is spawned it calls load_alarms/3 callback with load_from set to nil.