can't run unit tests with jest when using esm modules, typescript and undici v5.16.0

[marinrusu1997]

Bug Description

When trying to run unit tests with jest for files which use undici an error is thrown.

Reproducible By

You can reproduce this error by cloning this repo. README contains steps to reproduce the bug.

Expected Behavior

Unit tests should complete successfully.

Logs & Screenshots

This is the error shown by jest:

 Must use import to load ES Module: /Users/marin/Development/jest-undici-esm-bug/node_modules/undici/lib/llhttp/llhttp.wasm

      at Runtime.requireModule (node_modules/jest-runtime/build/index.js:817:21)
          at async Promise.all (index 0)
          at async Promise.all (index 0)

Also notice that if you lower the undici version, let's say to v5.15.0, a different issue will be thrown

/Users/marin/Development/jest-undici-esm-bug/node_modules/undici/lib/client.js:1184
        if (socket[kParser].timeoutType !== TIMEOUT_IDLE) {
                            ^

TypeError: Cannot read properties of undefined (reading 'timeoutType')
    at _resume (/Users/marin/Development/jest-undici-esm-bug/node_modules/undici/lib/client.js:1184:29)
    at resume (/Users/marin/Development/jest-undici-esm-bug/node_modules/undici/lib/client.js:1148:3)
    at connect (/Users/marin/Development/jest-undici-esm-bug/node_modules/undici/lib/client.js:1133:3)

Environment

MacOS Monterey
Node v16.14.2
Undici v5.16.0

[KhafraDev]

edit: see #1878 (comment) for a better solution!

This is an issue with jest.config.cjs:

diff --git a/jest.config.cjs b/jest.config.cjs
index 3841fe0..cb6e7d5 100644
--- a/jest.config.cjs
+++ b/jest.config.cjs
@@ -8,7 +8,7 @@ module.exports = {
                },
        },
        moduleNameMapper: {
-               '^(\\.{1,2}/.*)\\.js$': '$1',
+               '^(\\.{1,2}/.*)\\.js$': '$1.js',
        },
        testMatch: ["**/test/**/*.spec.ts"]
-};
\ No newline at end of file
+};
diff --git a/test/index.spec.ts b/test/index.spec.ts
index 87d3dbb..9068d1f 100644
--- a/test/index.spec.ts
+++ b/test/index.spec.ts
@@ -7,7 +7,7 @@ describe('get request', function () {
     afterAll(stopServer);

     it('makes get request', async () => {
-        const result = await get(BASE_URL);
+        const result = await (await get(BASE_URL)).body.text();
         expect(result).toBe('Hello World');
     });
 })

I would experiment with moduleNameMapper more as it might conflict with other requires/imports/whatever it's used for. The issue is that it would change './llhttp/llhttp.wasm.js' to './llhttp/llhttp.wasm', which caused the require to fail, for whatever reason. Who knows with jest?

[KhafraDev]

Okay, it seems like ts-jest is at fault for suggesting a bad default for moduleNameWrapper.

[cwilso03]

Yeah, ts-jest's suggestion is to just drop the .js suffix on imports so Jest doesn't complain about the ESM import syntax.

To fix this in my project, I changed my jest.config.js file to specifically exclude llhttp.wasm.js from that modification, like so:

  moduleNameMapper: {
    '^(\\.{1,2}/.*/llhttp\\.wasm\\.js)$': '$1',
    '^(\\.{1,2}/.*)\\.js$': '$1'
  },

It's a bit of a hack, but until Jest has full ESM support, it gets the job done.

To help future searchers, I should note, I was led to this issue while trying to debug this problem when importing @elastic/elasticsearch. They're apparently using Undici somewhere in their dependency tree. As with the original poster, the problem only appeared with my Jest ts-jest ESM tests, and not with my actual codebase (which is ESM/TypeScript).