Tests are failing after upgrade to 0.8.1

[just-boris]

If you are reporting a bug, please fill in below. Otherwise feel free to remove this template entirely.

Can you reproduce the problem with latest npm?

I have Yarn installed, so CRA used latest yarn@0.18.0 to setup.

Description

My test command fails with the following error

 FAIL  src/App.test.js
  ● Test suite failed to run

    TypeError: /home/bserdiuk/coding/test/src/App.test.js: Cannot read property 'length' of null
      
      at Buffer._append (node_modules/babel-generator/lib/buffer.js:83:25)
      at Buffer.append (node_modules/babel-generator/lib/buffer.js:55:10)
      at Generator._append (node_modules/babel-generator/lib/printer.js:206:52)
      at Generator.word (node_modules/babel-generator/lib/printer.js:131:10)
      at Generator.Identifier (node_modules/babel-generator/lib/generators/types.js:38:8)
      at node_modules/babel-generator/lib/printer.js:298:23
      at Buffer.withSource (node_modules/babel-generator/lib/buffer.js:142:28)
      at Generator.withSource (node_modules/babel-generator/lib/printer.js:189:15)
      at Generator.print (node_modules/babel-generator/lib/printer.js:297:10)
      at Generator.VariableDeclarator (node_modules/babel-generator/lib/generators/statements.js:309:8)

It worked fine with version 0.7.0, today I tried to upgrade to latest 0.8.1 and got the error above.
I have generated new test application with latest create-react-app and react-scripts and could find a minimal example to reproduce.

Add the following test in your test files, then run npm test.

it('async test', async () => {
    const {result} = doSometing();
});

Basically, destructuring assignment doesn't work in async function with Jest.
Babel Repl transpiles this code fine. Also it works fine if I will put this code into source. Problem appears only in testing code.

Expected behavior

I expect that it works as it was before in 0.7.0

Actual behavior

Tests are not run, error appears before any test starts.

Environment

Run these commands in the project folder and fill in their results:

1. npm ls react-scripts (if you haven’t ejected):

npm ls react-scripts
test@0.1.0 /home/bserdiuk/coding/test
└── react-scripts@0.8.1 

2. node -v:

v6.9.1

3. npm -v:

4.0.3

Then, specify:

1. Operating system: Ubuntu 16.04.1 LTS
2. Browser and version: not applicable

[EnoahNetzach]

probably related: #1160

[just-boris]

I was following the discussion in the thread #1160 and believe that my problem is also related to mentioned Babel issue: babel/babel#4759

Also, I have found that it was introduced by updating preset:
#1051

Now there are less Babel plugins applied in test environment, but some of them can't still have implicit dependencies on other transformations that was excluded now.

@gaearon could you consider rolling this PR back to work around the issue?

[EnoahNetzach]

@just-boris yep, that's exactly what we were finding out in #1160, also.

So, yep, my advise is that we either:

• rollback to using babel-preset-latest instead of babel-preset-env
• manually add the "missing" plugins

I'd prefer the first solution.

[gaearon]

I'm happy to push a fix but I want to have an actionable plan for re-enabling -env preset so that we can keep track of all issues and know when it's safe to re-enable. Kinda like we have a list in #553 (comment).

manually add the "missing" plugins

I would prefer this to enabling all of them. There are speed improvements from disabling most transforms, and I don't want to lose them. If something is missing we'll learn about it and file more Babel bugs. It's better than not knowing and learning that the next time we try to enable -env.

Would you like to make a PR for adding missing plugins?

[gaearon]

Also, would that help as a temporary workaround?
babel/babel#4759 (comment)

[EnoahNetzach]

It doesn't seem to work in my case..

[hzoo]

Just saw this - so tried to repro from scratch

npm install -g create-react-app
create-react-app my-app
cd my-app/
npm start

I added a test to App.test.js

it('async test', async () => {
    const {result} = Promise.resolve({ result: 1});
});

and it passes for me with yarn run test on yarn 0.17.4 and node 6.9.0

but maybe it was just that code?

[hzoo]

env means that you shouldn't need regenerator at all because you are using -env? (which just uses async-to-gen)

[EnoahNetzach]

@hzoo the problem seems to arise when babel-jest tries to transpile code, not while running the proper tests (I'm not entirely sure, as I don't know exactly how it works).

Try this.