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reduce.spec.js
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reduce.spec.js
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import { add } from './add.js'
import { concat } from './concat.js'
import { reduce, reduceStopper } from './reduce.js'
const reducer = (
prev, current, i
) => {
expect(i).toBeNumber()
return prev + current
}
const initialValue = 1
const list = [ 1, 2, 3 ]
const ERROR = 'reduce: list must be array or iterable'
test('happy', () => {
expect(reduce(
reducer, initialValue, list
)).toBe(7)
})
test('with object as iterable', () => {
expect(() =>
reduce(
reducer, initialValue, {
a : 1,
b : 2,
}
)).toThrowWithMessage(TypeError, ERROR)
})
test('with undefined as iterable', () => {
expect(() => reduce(
reducer, 0, {}
)).toThrowWithMessage(TypeError, ERROR)
})
test('with reduceStopper', () => {
let maxIndex
const reducer = (
prev, current, i
) => {
maxIndex = i
return current === 2 ? reduceStopper(current) : prev
}
expect(reduce(
reducer, initialValue, list
)).toBe(2)
expect(maxIndex).toBe(1)
})
test('returns the accumulator for a null list', () => {
expect(reduce(
add, 0, null
)).toBe(0)
expect(reduce(
concat, [], null
)).toEqual([])
})
test('returns the accumulator for an undefined list', () => {
expect(reduce(
add, 0, undefined
)).toBe(0)
expect(reduce(
concat, [], undefined
)).toEqual([])
})