Warn if describe returns a value

[jeysal]

Summary

As the troubleshooting docs state, tests must be defined synchronously. This PR aims to prevent a class of errors where describe is used with an async function by printing a dedicated error message instead of "Your test suite must contain at least one test)", which usually appears if something is awaited before the it calls.

Would have saved these people.
Unfortunately does not protect against this one though, and we'd need static analysis to save people from top-level awaits.

This could be considered breaking, especially if someone can think of a legitimate use case for returning a Promise (or anything at all) from describe. Or it could be considered non-breaking because returning a Promise (or anything at all) from describe was never supported. Hopefully FB doesn't do it 😅

Test plan

New e2e test green with and without JEST_CIRCUS=1.

[jeysal]

Just noticed overrideGlobals is failing, will take care of that.

[SimenB]

This could be considered breaking, especially if someone can think of a legitimate use case for returning a Promise (or anything at all) from describe

It probably is - we had a test at work with an async describe which worked (we didn't await anything, so it was able to run within a tick or whatever). I'm fine with it though - the fix is for people to just delete it (and they should use https://github.com/jest-community/eslint-plugin-jest/blob/master/docs/rules/valid-describe.md)

[jeysal]

I've updated the PR to only console.warn for now.
Will create an issue for failing in Jest 25 once this is merged

[jeysal]

Added an ugly stack trace:

Unfortunately couldn't find an easy way to print a nice one in those files, but at least it does contain the describe location. @SimenB if you can find us a ProjectConfig, jest-message-util would of course be a lot prettier 😄
When changing from console.warn to throwing, the error will be pretty automatically

[jeysal]

Update: error stack now prettier

[jeysal]

Jasmine

Circus

[jeysal]

Updated e2e tests to snapshot stdout instead of just matching a few of the lines. I think this is ready now

[codecov-io]

Codecov Report

Merging #7852 into master will increase coverage by 0.77%.
The diff coverage is 21.42%.

@@            Coverage Diff             @@
##           master    #7852      +/-   ##
==========================================
+ Coverage   63.31%   64.09%   +0.77%     
==========================================
  Files         263      264       +1     
  Lines       10266    10218      -48     
  Branches     2098     1836     -262     
==========================================
+ Hits         6500     6549      +49     
+ Misses       3273     3262      -11     
+ Partials      493      407      -86

Impacted Files	Coverage Δ
packages/jest-circus/src/index.ts	68.05% <0%> (-4.01%)	⬇️
packages/jest-jasmine2/src/jasmine/Env.js	0% <0%> (ø)	⬆️
packages/jest-util/src/isPromise.ts	100% <100%> (ø)
packages/expect/src/jasmineUtils.ts	83.92% <0%> (-0.9%)	⬇️
packages/jest-haste-map/src/index.ts	83.28% <0%> (-0.05%)	⬇️
packages/jest-watcher/src/PatternPrompt.ts	0% <0%> (ø)	⬆️
packages/jest-runtime/src/index.ts	68.98% <0%> (ø)	⬆️
packages/jest-changed-files/src/index.ts	0% <0%> (ø)	⬆️
packages/jest-matcher-utils/src/index.ts	91.83% <0%> (ø)	⬆️
packages/jest-circus/src/formatNodeAssertErrors.ts	14.28% <0%> (ø)	⬆️
... and 72 more

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[SimenB]

@thymikee thoughts?

[thymikee]

Love it. I'm thinking that maybe it would be better to leave the warning title yellow and the rest of the message (or at least code frame) in default color?

[SimenB]

It's yellow due to console.warn. Could use console.log? I don't think that messes with colors

[thymikee]

I'd go with console.log and yellow heading. Yellow codeframe feels odd, and it's something we don't do anywhere else in the code, right? Although jest-validate's warnings are whole yellow, so maybe let's just do chalk.reset on the code frame

[jeysal]

New warnings for
Jasmine

Circus

[SimenB]

Cool! Should hold off on merging this until we land the massive #7970

[SimenB]

Rebase now that we've merged the jasmine PR? 🙂

[jeysal]

Aye

[github-actions]

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