How can I test if a function was called?

// builder.js
const toLowerCase = (value) => value.trim().toLowerCase()

class Builder {
  build = (value) => toLowerCase(value)
}

export default Builder

export { toLowerCase }

// builder.test.js
import Builder, { toLowerCase } from './builder.js'

describe('Builder', () => {
  it('should build trimmed lowercase string', () => {
    jest.spyOn(toLowerCase, 'call')    
    Builder.build(' Data ')
    expect(toLowerCase).toHaveBeenCalled()
  })
})