panic: testing: Verbose called before Init case in Go

Trying to run https://github.com/adonovan/gopl.io/blob/master/ch8/cake/cake_test.go

but got

panic: testing: Verbose called before Init

goroutine 1 [running]:
testing.Verbose(...)
  /usr/lib/go-1.17/src/testing/testing.go:453
.../cake_test.init()

It says the error comes from cake_test.init(), yet the cake_test.go file doesn't contain init():

$ grep init cake_test.go | wc
      0       0       0

What exactly is the problem?

For this specific case, adding Init() function did the trick.

var defaults cake.Shop

func Init() {
    defaults = cake.Shop{
        Verbose:      testing.Verbose(),
        Cakes:        20,
        BakeTime:     10 * time.Millisecond,
        NumIcers:     1,
        IceTime:      10 * time.Millisecond,
        InscribeTime: 10 * time.Millisecond,
    }
}