Ignite: Jest tests run against local code, not against the bundle

[aschrijver]

Local project files are used for Jest tests, not transpiled bundle code

---

I have created a project using the standard boilerplate, then added babel-plugin-module-resolver: "2.7.1"to the package and in.babelrc`:

  "plugins": [
    ["module-resolver", {
      "alias": {
        "mock": "./config/mock",
        "fs": "./config/mock",
        "sodium-universal": "libsodium",
        "crypto": "react-native-crypto",
        "path": "path-browserify"
      }
    }]
  ]

This because I have some node-based dependencies (without UI) that I want to reuse in my RN app.
With this plugin Babel neatly replaces imports and requires throughout node_modules.

When running the emulator I get an error complaining that fs.readFileSync is undefined, which is completely expected, as fs is just a mock, but is invoked from one of those node-related dependencies.

Now when running Jest unit tests that invoke the same methods, using yarn test (defined as "NODE_ENV=test jest --no-cache" in package.json) or in any other way I could think of, the tests succeed, where they should also fail!

So seems like Jest is completely ignoring the bundle and happily uses the original sources from disk.

---

Steps to reproduce:

• Create new Ignite project
• Add babel-plugin-module-resolver and .babelrc
• Point alias fs to an empty js file
• Invoke readFileSync in App

- Create and run a test

ignite doctor results:

System
  platform           linux                                                                                                
  arch               x64                                                                                                  
  cpu                4 cores       Intel(R) Core(TM) i7-4500U CPU @ 1.80GHz  

JavaScript
  node               7.10.1       /usr/local/bin/node  
  npm                4.2.0        /usr/local/bin/npm   
  yarn               0.24.6       /usr/bin/yarn        

React Native
  react-native-cli   2.0.1       
  app rn version     0.45.1      

Ignite
  ignite             2.0.0        /usr/local/bin/ignite  

Android
  java               1.8.0_111    /usr/bin/java  
  android home       -            undefined 

PS. This may be more of a Jest or babel-jest issue, but I'm filing here to start with :)

[skellock]

Do you experience the same issue without ignite as well? react-native init Strangeness --version 0.45.1

[aschrijver]

If you mean after entering react-native init Strangeness --version 0.45.1 and yarn test, then yes the results are the same.

[skellock]

Gotcha. I'll close this up as this isn't actionable on our end.

If you do get some answers though, I'd love to hear how this gets solved. Maybe a mockfs library or something?

[aschrijver]

Thanks, I'll report back.

[aschrijver]

Hi @skellock
I received a response from the Jest team, but I don't understand it.

This is the expected behavior. Jest is supposed to run on source files. On any large codebase, generating a bundle before running tests is too slow, so Jest compiles files just-in-time, which makes it fast.

Have asked for more info. Could you have a quick look as well? Thanks.
https://github.com/facebook/jest/issues/4028#issuecomment-315273833

[aschrijver]

@skellock I did not receive any more help from Jest team. Going to switch to mocha, jasmine and/or karma. Thanks for your help earlier!

[skellock]

Sorry man. I know how frustrating it can be when you don’t get any answers.

[aschrijver]

Ah that's all-right. Its also part of an average developers' life. We should just live with that.. :wink:

[aschrijver]

PS I left a pointer on SO for someone who wants to harvest some reputation by solving this issue: https://stackoverflow.com/questions/45056952/debugging-jest-unit-tests-with-breakpoints-in-vs-code-with-react-native/45073796#comment77211417_45073796