CRA You need Jest version >= 22.0.0 to use Stryker error

[protosimon]

First of all, I am elated to find a mutation test framework for JS. I come from a quick check and PIT testing background and place a high value on the quality of tests. I am trying to configure stryker with my CRA project and getting the following error even-though the peer dependencies are met. An entry in the CRA docs on how to configure stryker would be great for devs and growing the community.

stryker.conf.js

 module.exports = function (config) {
  config.set({
    jest: {
      project: 'react'
    },
    testRunner: 'jest',
    mutator: 'javascript',
    coverageAnalysis: 'off',
    mutate: ['src/**/*.js']
  });
};

I have the following dependencies and jest config in package.json

 "devDependencies": {
    "axe-testcafe": "^1.1.0",
    "axios-mock-adapter": "^1.12.0",
    "chalk": "^2.4.0",
    "enzyme": "^3.3.0",
    "enzyme-adapter-react-16": "^1.1.1",
    "eslint": "~4.12.1",
    "eslint-config-react-app": "^2.1.0",
    "eslint-plugin-testcafe": "^0.2.1",
    "flow-bin": "~0.70.0",
    "flow-typed": "2.4.0",
    "gulp": "^3.9.1",
    "gulp-maven-deploy": "~0.2.0",
    "jest-emotion": "^9.0.0-0",
    "react-scripts": "1.1.4",
    "redux-devtools-extension": "^2.13.2",
    "stryker": "0.21.0",
    "stryker-api": "0.15.0",
    "stryker-jest-runner": "^0.7.0",
    "testcafe": "^0.19.2"
  },
  "jest": {
    "collectCoverageFrom": [
      "src/**/*.js",
      "!**/mock-backend/**",
      "!**/types/**"
    ]
  }

[mthmulders]

Hi @protosimon, thanks for taking the time to report this. Can you please do an npm ls jest to verify which version of Jest you're using?

[protosimon]

@mthmulders, I am using jest@20.0.4 that's pulled down by react-scripts.

[mthmulders]

Thanks! Didn't know they had v20. I'm using the TypeScript-flavour of CRA, which has v22.
It seems to me that CRA has had a Jest upgrade recently, but unfortunately it has not been released yet?

[nicojs]

I guess not:

We've overlooked this.

@mthmulders how much work would it be to also support v20?

[mthmulders]

Oh, CRA has a next branch, which has Jest 22, and a master (probably used for releases) which has Jest 20. Who'd have known...

We had a good reason to bump Jest to 20: Jest #5401 was biting us when we tried to run Jest from Stryker. I have no clue what it would take to downgrade Jest back to 22, since the general remark seems to be to "just upgrade Jest" :-(

[mthmulders]

You might try to use stryker-jest-runner@0.6.0, stryker-api@0.13.0 and stryker@0.19.1 in the meantime, and see if that works. The difference between stryker-jest-runner@0.6.0 and stryker-jest-runner@0.7.0 is that it bumps stryker-api and adds support for the TypeScript-flavour of CRA.
Can you see if that works for you?

[nicojs]

I'm no react expert, but can't @protosimon just install a new version of Jest? Sure he would have 2 jest versions in his node_modules (one node_modules/jest (v22) and one node_modules/react-scripts/jest (v20)), but that shouldn't be a problem right?

[mthmulders]

Since he's using CRA, I think he cannot. Quoting @gaearon in facebook/jest #5119:

It is not supported to update Jest manually in a CRA project.

[nicojs]

The way I see it, your not upgrading the react-scripts version of jest, instead installing a brand new one right next to it.

It seems to work for me:

npx create-react-app my-app
cd my-app
npm i -D jest@22
npm ls | grep jest

# ... outputs:
+-- jest@22.4.3
# ...
  +-- jest@20.0.4
# ...
stryker init
# < choose jest, no transpilers >
vi stryker.conf.js
# < change some things: mutate array (only mutate App.js), disable coverage analysis >
stryker run
[2018-05-17 09:55:58.040] [INFO] ConfigReader - Using stryker.conf.js in the current working directory.
[2018-05-17 09:55:58.384] [INFO] InputFileResolver - Found 1 of 15 file(s) to be mutated.
[2018-05-17 09:55:58.389] [INFO] InitialTestExecutor - Starting initial test run. This may take a while.
[2018-05-17 09:56:03.485] [INFO] InitialTestExecutor - Initial test run succeeded. Ran 1 tests in 5 seconds.
[2018-05-17 09:56:03.523] [INFO] Stryker - 1 Mutant(s) generated
[2018-05-17 09:56:03.527] [INFO] SandboxPool - Creating 8 test runners (based on CPU count)
Mutation testing  [==================================================] 100% (ETC 0.0s) 1/1 tested (0 survived)

Ran 0.00 tests per mutant on average.
----------|---------|----------|-----------|------------|----------|---------|
File      | % score | # killed | # timeout | # survived | # no cov | # error |
----------|---------|----------|-----------|------------|----------|---------|
All files |  100.00 |        0 |         1 |          0 |        0 |       0 |
 App.js   |  100.00 |        0 |         1 |          0 |        0 |       0 |
----------|---------|----------|-----------|------------|----------|---------|
[2018-05-17 09:56:18.815] [INFO] Stryker - Done in 20 seconds.
...

@protosimon could you give it a go?

[nicojs]

Closing it for now. Please comment again when you still have problems.