How to use checkForCommonEnvironmentErrors method in Jest

To check if expected object is a subset of the received object you need to use toMatchObject(object) method:

expect(parseTime('12:54')).toMatchObject({ hours: 12, minutes: 54})

or expect.objectContaining(object) matcher:

expect(parseTime('12:54')).toEqual(expect.objectContaining({ hours: 12, minutes: 54}))

they works in slightly different ways, please take a look at What's the difference between '.toMatchObject' and 'objectContaining' for details.

toContain() is designed to check that an item is in an array.

You appear to have placed both your code and test files in the same directory (__tests__/sum.js and __tests__/sum.test.js). I don't think that's a specific reason for the failure you are seeing but its not the convention.

It should not be necessary to specify a folder to search unless your project is complete. Run jest without any arguments, other than necessary options, and it will search the current directory an below.

The convention is either:

/root
  /src
    sum.js
    /__tests__
      sum.js

or:

/root
  /src
    sum.js
    sum.test.js

You can use test or spec in the latter example. root and src are up to you, root is normally the location of package.json and is where you invoke jest from (e.g. myApp). src help differentiate from other app components like build and assets.

Works for me with the following settings.

// package.json

"jest": {
  "scriptPreprocessor": "preprocessor.js",
  "unmockedModulePathPatterns": [
    "react"
  ],
  "setupEnvScriptFile": "before_test.js"
}

// preprocessor.js

var ReactTools = require('react-tools');

module.exports = {
    process: function(src) {
        return ReactTools.transform(src);
    }
};

// before_test.js

React = require("react"); // Global React object

Jest is installed, but is likely in your ./node_modules/.bin directory. You can append that to your command ./node_modules/.bin/jest --updateSnapshot. Since you already have jest as a scripts command in your package.json you can also run it with npm test -- --updateSnapshot. npm automatically adds ./node_modules/.bin to your path.

update: Newer versions of yarn will resolve node module bin scripts, so you can also just run yarn jest {cmd} and it should work.

I didn't know about lint-staged. I'll give it a try. I looked for this a while ago.

Have you tried?

"jest --bail --coverage --findRelatedTests",

Jest docs say that findRelatedTests can be used together with --coverage to include a test coverage for the source files, no duplicate --collectCoverageFrom arguments needed.

Should work but I haven't tried.

I've had very similar error, but in my case default VSCode TypeScript formatter was messing with braces. In .vscode/settings.json add:

"javascript.format.insertSpaceAfterOpeningAndBeforeClosingEmptyBraces": false,
"typescript.format.insertSpaceAfterOpeningAndBeforeClosingEmptyBraces": false,

You might also find useful option:

"[typescript]": {
    "editor.defaultFormatter": "dbaeumer.vscode-eslint"
}

As far as I know this is not easily possible, though a couple of places to look for more information (not out of the box):

Jest allows to use custom reporters: https://jestjs.io/docs/en/configuration.html#reporters-array-modulename-modulename-options , so you can write your own reporter and display output differently. At the moment though you don't get updates for separate tests, just test suits, here is an issue created by Dan Abramov: https://github.com/facebook/jest/issues/6616 .

From the github thread above - Reporter interface for now looks like:

export default class BaseReporter {
  onRunStart(results: AggregatedResult, options: ReporterOnStartOptions) {}

  // these are actually for the test suite, not individual test results
  onTestStart(test: Test) {}
  onTestResult(test: Test, testResult: TestResult, results: AggregatedResult) {}

  onRunComplete(contexts: Set<Context>, results: AggregatedResult ): ?Promise<void> {}
}

I didn't find a predefined way to pass parameters from test though into the testResult object. So you are mostly limited to logging information based on test names. Below is an example of testResult property inside testResult object:

testResults:
  [ { ancestorTitles: [Array],
       duration: 5,
       failureMessages: [],
       fullName: 'add should add two numbers',
       location: null,
       numPassingAsserts: 0,
       status: 'passed',
       title: 'should add two numbers' } ],

As you can see this is all the information standard reporter uses: test name, duration, status. For reference the default reporter is here: https://github.com/facebook/jest/blob/7b7fd01350/packages/jest-cli/src/reporters/default_reporter.js

Update all gatsby plugins to the latest & follow this source

It worked for me ????

Jest is throwing this error Matcher error: received value must be a promise because in expect you are just passing the function reference. Without () - action is just a function reference it will not return anything.

To fix this issue you have to call the function in expect like action() so it will return the promise object.

And the second part, you have to throw error like. Promise.reject(new Error('some error')); in the reject so the tothrow condition can be full filled.

Example:

function hostelService() {
   return Promise.reject(new Error('some error'));
}

const action = async () => {
   await hostelService();
};

it( "Should throw the error", async () => {
   await expect(action()).rejects.toThrow('some error');
});

Hope this will be helpful.