Proper Jest configuration with React-native 0.56 - react-native

Question

After upgrading to react-native 0.56 I'm experiencing tons of babel reated errors on jest specs that used to run just fine.
I realize that react-native 0.56 requires babel7 and that's probably related but I don't have enough experience/understaanding in babel to figure out what I'm missing.
Some error examples:
/xxx/spec/Bootstrap.test.js:6
import thunk from 'redux-thunk';
^^^^^
SyntaxError: Unexpected identifier
at ScriptTransformer._transformAndBuildScript (node_modules/jest-runtime/build/script_transformer.js:403:17)
another:
import { rootReducer } from '../store';
^
SyntaxError: Unexpected token {
at ScriptTransformer._transformAndBuildScript (node_modules/jest-runtime/build/script_transformer.js:403:17)
My package.json jest config is as follows:
"jest": {
"preset": "react-native",
"collectCoverage": true,
"coverageReporters": [
"cobertura",
"lcov"
],
"coverageDirectory": "coverage",
"globals": {
"__TEST__": true
},
"moduleNameMapper": {
"styled-components": "<rootDir>/node_modules/styled-components/dist/styled-components.native.cjs.js"
},
"moduleDirectories": [
"node_modules",
"/"
],
"transformIgnorePatterns": [
"node_modules/(?!react-native|react-navigation)/"
],
"setupFiles": [
"jest-localstorage-mock",
"./node_modules/appcenter/test/AppCenterMock.js",
"./node_modules/appcenter-analytics/test/AppCenterAnalyticsMock.js",
"./node_modules/appcenter-crashes/test/AppCenterCrashesMock.js"
]
},
.babelrc is defined as follows:
{
"presets": ["react-native"],
"env": {
"development": {
"plugins": ["transform-class-properties"]
},
"test": {
"plugins": ["transform-class-properties"]
}
}
}
I also have the following devdependencies:
"#babel/core": "^7.0.0-beta.52",
"babel-core": "^7.0.0-beta.52",
"babel-eslint": "~8.2.5",
"babel-plugin-module-resolver": "^3.1.1",
"babel-plugin-transform-class-properties": "~6.24.1",
"babel-plugin-transform-decorators-legacy": "^1.3.5",
"babel-preset-expo": "~4.0.0",
"babel-preset-react-native": "^5.0.1",
"babel-preset-react-native-stage-0": "^1.0.1",
"babel-preset-stage-0": "^6.24.1",
I've tried several approaches but couldn't progress much.
Besides the jest environment, the application runs fine.

Answer 1

Details of the workaround I did to move on, while 0.57 wasn't ready:
Basically I had to create 2 config files:
jest-acceptance.config (with the following relevant snippets)
"preset": "react-native",
"transform": {
"^.+\\.js$": "<rootDir>/custom_b7_processor.js"
},
"testRegex": "(/test/.*|(\\.|/)spec)\\.js$",
jest-unit.config (with the following relevant snippets)
"preset": "react-native",
"testRegex": "(/test/.*|(\\.|/)test)\\.js$",
That custom_b7_processor, is some sort of internal code from react-native:
/**
* Copyright (c) 2015-present, Facebook, Inc.
*
* This source code is licensed under the MIT license found in the
* LICENSE file in the root directory of this source tree.
*
* #format
* #flow
*/
/* eslint-disable */
'use strict';
const {transformSync: babelTransformSync} = require('#babel/core');
/* $FlowFixMe(>=0.54.0 site=react_native_oss) This comment suppresses an error
* found when Flow v0.54 was deployed. To see the error delete this comment and
* run Flow. */
const babelRegisterOnly = require('metro-babel-register');
/* $FlowFixMe(>=0.54.0 site=react_native_oss) This comment suppresses an error
* found when Flow v0.54 was deployed. To see the error delete this comment and
* run Flow. */
const createCacheKeyFunction = require('fbjs-scripts/jest/createCacheKeyFunction');
const generate = require('#babel/generator').default;
const nodeFiles = RegExp(
[
'/local-cli/',
'/metro(?:-[^/]*)?/', // metro, metro-core, metro-source-map, metro-etc
].join('|'),
);
const nodeOptions = babelRegisterOnly.config([nodeFiles]);
babelRegisterOnly([]);
/* $FlowFixMe(site=react_native_oss) */
const transformer = require('metro/src/reactNativeTransformer');
module.exports = {
process(src /*: string */, file /*: string */) {
if (nodeFiles.test(file)) {
// node specific transforms only
return babelTransformSync(
src,
Object.assign(
{filename: file},
{sourceType: 'script', ...nodeOptions, ast: false},
),
).code;
}
const {ast} = transformer.transform({
filename: file,
localPath: file,
options: {
ast: true, // needed for open source (?) https://github.com/facebook/react-native/commit/f8d6b97140cffe8d18b2558f94570c8d1b410d5c#r28647044
dev: true,
inlineRequires: true,
platform: '',
projectRoot: '',
retainLines: true,
sourceType: 'unambiguous', // b7 required. detects module vs script mode
},
src,
plugins: [
[require('#babel/plugin-transform-block-scoping')],
// the flow strip types plugin must go BEFORE class properties!
// there'll be a test case that fails if you don't.
[require('#babel/plugin-transform-flow-strip-types')],
[
require('#babel/plugin-proposal-class-properties'),
// use `this.foo = bar` instead of `this.defineProperty('foo', ...)`
{loose: true},
],
[require('#babel/plugin-transform-computed-properties')],
[require('#babel/plugin-transform-destructuring')],
[require('#babel/plugin-transform-function-name')],
[require('#babel/plugin-transform-literals')],
[require('#babel/plugin-transform-parameters')],
[require('#babel/plugin-transform-shorthand-properties')],
[require('#babel/plugin-transform-react-jsx')],
[require('#babel/plugin-transform-regenerator')],
[require('#babel/plugin-transform-sticky-regex')],
[require('#babel/plugin-transform-unicode-regex')],
[
require('#babel/plugin-transform-modules-commonjs'),
{strict: false, allowTopLevelThis: true},
],
[require('#babel/plugin-transform-classes')],
[require('#babel/plugin-transform-arrow-functions')],
[require('#babel/plugin-transform-spread')],
[require('#babel/plugin-proposal-object-rest-spread')],
[
require('#babel/plugin-transform-template-literals'),
{loose: true}, // dont 'a'.concat('b'), just use 'a'+'b'
],
[require('#babel/plugin-transform-exponentiation-operator')],
[require('#babel/plugin-transform-object-assign')],
[require('#babel/plugin-transform-for-of'), {loose: true}],
[require('#babel/plugin-transform-react-display-name')],
[require('#babel/plugin-transform-react-jsx-source')],
],
});
return generate(
ast,
{
code: true,
comments: false,
compact: false,
filename: file,
retainLines: true,
sourceFileName: file,
sourceMaps: true,
},
src,
).code;
},
getCacheKey: createCacheKeyFunction([
__filename,
require.resolve('metro/src/reactNativeTransformer'),
require.resolve('#babel/core/package.json'),
]),
};
At my .babelrc I had to include the following:
"presets": ["./node_modules/babel-preset-react-native-b6"],
That is pointing to a fork I made of the babel preset that React-native was using at 0.56-
https://github.com/lhrolim/babel-preset-react-native.
At my package.json I had te following babel dependencies
"babel-preset-react-native": "~5.0.2",
"babel-preset-react-native-b6": "github:lhrolim/babel-preset-react-native",
The test scripts I used then:
"test": "npm run test-acc && npm run test-unit",
"test-acc": "jest --config=jest_acceptance-config.json",
"test-unit": "jest --config=jest_unit-config.json",
I believe there might be some redundancies here and there, but that's what worked for me.