check-promise.md

const assert = require('assert')
const BLUEBIRD = require('bluebird')

const nameAsync1 = async (name) => name
const nameAsync2 = (name) => Promise.resolve(name)
const nameAsync3 = (name) => BLUEBIRD.resolve(name)
const nameSync = (name) => name

const isPromise1 = (value) => Promise.resolve(value) === value
const isPromise2 = (value) => BLUEBIRD.resolve(value) === value

assert(isPromise1(nameAsync1('thomas')) === true, 'async function is native promise')
assert(isPromise1(nameAsync2('thomas')) === true, 'native promise resolved is native promise')
assert(isPromise1(nameAsync3('thomas')) === true, 'bluebird resolved promise is native promise')

assert(isPromise2(nameAsync1('thomas')) === true, 'async function is bluebird promise')
assert(isPromise2(nameAsync2('thomas')) === true, 'native promise resolved is bluebird promise')
assert(isPromise2(nameAsync3('thomas')) === true, 'bluebird resolved promise is bluebird promise')

// console.log(isPromise1(nameSync('thomas')))
// console.log(isPromise2(nameSync('thomas')))

// console.log(isPromise1({ then: () => {} }))
// console.log(isPromise2({ then: () => {} }))

This doesn't make sense to me. You're executing the function to check if it's a promise.
You can simply do Promise.resolve(fn()).then(...) in your code; to ensure it's a promise.
Why would you ever need this?

@onury Sometimes you need to do different things for promises. You also can do things differently when things are not promises: like synchronously inspect their value.