Jest: Expose the line number of a failing test block in output

[sharmilajesupaul]

I'm trying to build an automated reporting tool that flags and skips flaky tests. It would be really helpful if Jest provided the line number for a failing test in the output file.

The script we're using to run generate the output file is:
jest --json --outputFile=./tmp/jest.json --silent .

cc. @gdborton, @ljharb

Do you want to request a feature or report a bug?
Feature

What is the current behavior?
The information in the output file for a failing test includes a stack trace but does not expose the line number of the failing test block.

What is the expected behavior?
Expose the starting line number of the failing test block. So I can append .skip to it blocks.

e.g. For this file:

// failing_spec.js
import { expect } from 'chai';

describe('Failing test', () => {
  it('should fail', () => {
    expect(false).to.equal(true);
  });
});

Diff of output with added lineNumber:

{
  "numFailedTestSuites": 1,
  "numFailedTests": 1,
  "numPassedTestSuites": 0,
  "numPassedTests": 0,
  "numPendingTestSuites": 0,
  "numPendingTests": 0,
  "numRuntimeErrorTestSuites": 0,
  "numTotalTestSuites": 1,
  "numTotalTests": 1,
  "snapshot":
  {
    "added": 0,
    "didUpdate": false,
    "failure": false,
    "filesAdded": 0,
    "filesRemoved": 0,
    "filesUnmatched": 0,
    "filesUpdated": 0,
    "matched": 0,
    "total": 0,
    "unchecked": 0,
    "unmatched": 0,
    "updated": 0
  },
  "startTime": 1509064905195,
  "success": false,
  "testResults": [
  {
    "assertionResults": [
    {
      "ancestorTitles": ["Failing test"],
      "failureMessages": ["AssertionError: expected false to equal true\n    at Object.<anonymous> (/failing_spec.js:5:33)\n    at Object.asyncFn (/node_modules/jest-jasmine2/build/jasmine_async.js:68:30)\n    at e (/node_modules/jest-jasmine2/build/queue_runner.js:47:12)\n    at mapper (/node_modules/jest-jasmine2/build/queue_runner.js:34:19)\n    at promise.then (/node_modules/jest-jasmine2/build/queue_runner.js:75:39)\n    at process._tickCallback (internal/process/next_tick.js:109:7)"],
      "fullName": "Failing test should fail",
+     "lineNumber": [4, 3],
      "status": "failed",
      "title": "should fail"
    }],
    "endTime": 1509064906822,
    "message": "\u001b[1m\u001b[31m  \u001b[1m● \u001b[1mFailing test › should fail\u001b[39m\u001b[22m\n\n    AssertionError: expected false to equal true\n\u001b[2m      \u001b[22m\n\u001b[2m      \u001b[2mat Object.<anonymous> (\u001b[2m\u001b[0m\u001b[36mspec/javascripts/failing_spec.js\u001b[39m\u001b[0m\u001b[2m:5:33)\u001b[2m\u001b[22m\n\u001b[2m      \u001b[2mat process._tickCallback (\u001b[2minternal/process/next_tick.js\u001b[2m:109:7)\u001b[2m\u001b[22m\n",
    "name": "/spec/javascripts/failing_spec.js",
    "startTime": 1509064905271,
    "status": "failed",
    "summary": ""
  }],
  "wasInterrupted": false
}

Please provide your exact Jest configuration and mention your Jest, node, yarn/npm version and operating system.

```js
// node: v6.11.1
// npm: 3.10.10

// jest config
{
"bail": false,
"collectCoverageFrom": [
"/app/assets/javascripts//.{js,jsx}",
"!/vendor/",
"!/node_modules/",
"!/lib/",
"!/spec/",
"!/public/",
"!script/",
"!/ext/",
"!test/",
"!coverage/",
"!/packages/",
"!/initializers/",
"!/javascripts/facebook.js",
"!/javascripts/deep_link/branchSdkLoader.js",
"!/javascripts/april_fools/",
],
"coverageReporters": ["json-summary", "lcov", "html"],
"testEnvironment": "node",
"rootDir": "..",
"roots": [
"./app/assets/javascripts",
"./spec/javascripts"
],
"setupTestFrameworkScriptFile": "/spec/jest/setupJest.js",
"testRegex": "spec/javascripts/.(\.|/|_)(test|spec)\.jsx?$",
"testURL": "https://foo.com",
"transform": {
"^.+\.jsx?$": "/node_modules/babel-jest"
}
}
````

[SimenB]

This sounds like a cool idea. A quick look seems to indicate that this information is not currently available, though. Jasmine would have to expose it.

https://github.com/jasmine/jasmine/issues/537

That issue links to a possible workaround overriding it, which we can maybe do. Instead of throwing an error, we can do V8 stack capture though. Probably opt-in as well to avoid the perf hit for everyone

@cpojer thoughts? I haven't dug far enough into it to see if it's possible, but based on https://github.com/agirorn/jasmine-slow-reporter it seems like it should be feasible (in the same way we alias it to test already)

[cpojer]

If it's easy to add and doesn't slow down Jest, I'm on board.

[SimenB]

PR: #4782

[jasonfb]

💯