CODEWITHSUNDEEP
javascriptjestjsisbn
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Reputation: 1663

Jest causing a module to disappear

I'm trying to write tests for an old codebase of mine. It uses the isbn package from NPM, which is tiny but does the trick. But whenever I write tests that involve the module, it disappears. That is to say - the value of the module is set to {}.

I've written up two files to try and isolate this issue. I just can't figure out how this test is failing.

First file, isbnTest.js:

const { ISBN } = require("isbn");

function isbnExists() {
  return ISBN !== undefined;
}

console.log(isbnExists());

module.exports = {
  isbnExists,
};

Pretty simple:

Running this file from the console logs

true

But what happens when we run this code from within Jest?

The second file, ./isbnTest.test.js:

const { isbnExists } = require("./isbnTest.js");

test("isbn should exist", () => {
  expect(isbnExists()).toBe(true);
});

When I run npm test with these two files, the test fails.

FAIL  

./isbnTest.test.js
  ✕ isbn should exist (4ms)

  ● isbn should exist

    expect(received).toBe(expected) // Object.is equality

    Expected: true
    Received: false

      2 |
      3 | test("isbn should exist", () => {
    > 4 |   expect(isbnExists()).toBe(true);
        |                        ^
      5 | });
      6 |

      at Object.<anonymous> (isbnTest.test.js:4:24)

  console.log isbnTest.js:7
    false

Test Suites: 1 failed, 1 total
Tests:       1 failed, 1 total

It seems as though Jest must be doing some custom importing stuff that's somehow missing this module. Almost like it's being replaced with an empty mock? But I really don't know.

I'd love to remove the isbn package from my program, but without any tests I don't feel confident that I can ensure I won't break anything.

EDIT:

A commenter has pointed out that this doesn't reproduce, which means there's something askew on my machine. Can anyone provide as guess as to what that might be? Deleting and reinstalling the NPM modules doesn't do the trick. I don't think I have any jest config files.

After some further investigation, the problem is being caused by this line in the module:

var exports = typeof window === 'object' && window ? window: module.exports;

If I comment that out, Jest picks it up fine.

Upvotes: 0

Views: 83

Answers (0)

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