javascript - Jest: How to test function that returns a function - Stack Overflow

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I have several functions I would like to test with Jest. All functions are functions that return functions.

A simple example:

export function csl(foo) {
  return function(bar) {
      return(bar)
     };
}

now I want to test if the input = the return is. I try it with:

  expect(() => csl("foo")).toBe("foo") // = received: [Function anonymous]

  expect(csl("foo")).toBe("foo") // = received: undefined

How I can test these functions?

I have several functions I would like to test with Jest. All functions are functions that return functions.

A simple example:

export function csl(foo) {
  return function(bar) {
      return(bar)
     };
}

now I want to test if the input = the return is. I try it with:

  expect(() => csl("foo")).toBe("foo") // = received: [Function anonymous]

  expect(csl("foo")).toBe("foo") // = received: undefined

How I can test these functions?

• javascript
• jestjs

Share Improve this question Follow edited Jul 2, 2019 at 8:07 skyboyer 23.8k77 gold badges6262 silver badges7171 bronze badges asked Jul 1, 2019 at 13:43 CkappoCkappo 59722 gold badges1010 silver badges2727 bronze badges 3

• @CodyＧ oh gods, no – VLAZ Commented Jul 1, 2019 at 13:56
• @VLAZ Agreed, I don't know what Ckappo wants by looking at the function and not the result from the function generated... but now I am realizing they might not know how to call a function. – Cody Geisler Commented Jul 1, 2019 at 14:08
• 1 @CodyＧ seems like a fairly standard test, with the only "twist" being that it's testing a function that returns a function. So it's just missing a second execution for the inner function. I went to check the Jest docs if there is any better way to do it and then to see if there is a CDN copy to demonstrate how to do it but Ji aSH answered in the mean time with basically what I wanted to say. Couldn't find a CDN copy to demonstrate better. – VLAZ Commented Jul 1, 2019 at 14:10

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1 Answer 1

Sorted by: Reset to default 9

You need to call the returned function

expect(csl("foo")("bar")).toBe("bar")
                 ^^^^^^^

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