Coverage downgraded 24.49% after switching from Jest ^18.1.0 to ^19.0.2

[lucasbento]

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

What is the current behavior?
Jest ^18.1.0 was reporting a coverage of 83.1% on Jest ^19.0.2 it reports only 58.6%, -24.49% of coverage between the versions, the report looks pretty much the same (see the images below).

If the current behavior is a bug, please provide the steps to reproduce and either a repl.it demo through https://repl.it/languages/jest or a minimal repository on GitHub that we can yarn install and yarn test.

To test on version 18.1.0:

1. Clone master of https://github.com/lucasbento/create-graphql;
2. yarn install && npm run bootstrap && npm test;
3. open ./packages/coverage/index.html.

To test on version 19.0.2 (aerogear/create-graphql#82):

1. Clone feature/upgradeAll of https://github.com/lucasbento/create-graphql;
2. yarn install && npm run bootstrap && npm test;
3. open ./packages/coverage/index.html.

What is the expected behavior?
The coverage should stay the same between versions.

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

npm: 3.10.10
yarn: 0.19.1
node: v6.9.5
OS: Mac OS X El Capitan 10.11.5 Also happening on CI (aerogear/create-graphql#83)

{
  "testEnvironment": "node",
  "testPathIgnorePatterns": [
    "/coverage/",
    "/dist/",
    "/generators/",
    "/node_modules/"
  ],
  "moduleDirectories": [
    "src",
    "node_modules"
  ],
  "coveragePathIgnorePatterns": [
    "/__tests__/",
    "/coverage/",
    "/dist/",
    "/generators/",
    "/node_modules/"
  ],
  "coverageDirectory": "./coverage/",
  "coverageReporters": [
    "lcov",
    "html"
  ],
  "collectCoverage": true,
  "collectCoverageFrom": [
    "**/**/*.js"
  ],
  "testPathDirs": [
    "generator/src",
    "create-graphql/src"
  ],
  "rootDir": "./packages/",
  "verbose": true
}

Version ^18.1.0

Version ^19.0.2

[aaronabramov]

this is likely related to some other packages that were updated (istanbul, babel)

if you look at the detailed coverage

the newer version does a better job instrumenting the file and taking into account additional lines (the red highlight is messed up because of all the babel transformation. we can't really do much about it yet 😞)

[lucasbento]

@DmitriiAbramov: thanks for answering back.

What can I do about it at the moment? Should this be considered a bug on Jest since it uses those packages? Should I open an issue somewhere else?

Thank you!

[aaronabramov]

@lucasbento i'd say it looks more like the issue was fixed, and now you get a more accurate coverage report :)
If you have a threshold on your CI it probably makes sense to lower it (if it's failing right now)

[lucasbento]

@DmitriiAbramov: alright, gonna close this issue and merge the PR.

Thank you again!

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