Coverage doesn't have "conditional assignment" into consideration

🐛 Bug Report

When an object is set like this:

const myObj = {
  myProp: myVariable === 'given expected value',
};

Jest (or maybe nyc?) is not considering it as a branch.

However if I do:

const myObj = {
  myProp: myVariable === 'given expected value' ? true : false,
};

This is considered as a branch…

To Reproduce

Steps to reproduce the behavior:

• yarn create react-app
• yarn add classnames
• Change the src/App.js to:

import classnames from 'classnames';
import React from 'react';
import logo from './logo.svg';
import './App.css';

function App({ test }) {
  const myClassName = {
    [test]: test === 'yeah'
  };

  return (
    <div className={classnames('App', myClassName)}>
      <header className="App-header">
        <img src={logo} className="App-logo" alt="logo" />
        <p>
          Edit <code>src/App.js</code> and save to reload.
        </p>
        <a
          className="App-link"
          href="https://reactjs.org"
          target="_blank"
          rel="noopener noreferrer"
        >
          Learn React
        </a>
      </header>
    </div>
  );
}

export default App;

• Change the src/App.test.js to:

import React from 'react';
import { render } from '@testing-library/react';
import App from './App';

test('renders learn react link', () => {
  const { container, getByText } = render(<App />);
  const linkElement = getByText(/learn react/i);
  expect(linkElement).toBeInTheDocument();
  expect(container).toMatchSnapshot();
});

• Run yarn test --coverage
• Verify that the coverage is still 100%:

Expected behavior

Link to repl or repo (highly encouraged)

https://github.com/mAiNiNfEcTiOn/jest-conditional-assignment-repro

envinfo

  System:
    OS: macOS 10.15.2
    CPU: (8) x64 Intel(R) Core(TM) i7-6700K CPU @ 4.00GHz
    Memory: 2.19 GB / 32.00 GB
    Shell: 5.7.1 - /bin/zsh
  Binaries:
    Node: 12.13.1 - /usr/local/bin/node
    Yarn: 1.19.1 - /usr/local/bin/yarn
    npm: 6.12.1 - /usr/local/bin/npm
  Managers:
    Homebrew: 2.2.2 - /usr/local/bin/brew
    pip2: 19.3.1 - /usr/local/bin/pip2
    pip3: 19.3.1 - /usr/local/bin/pip3
    RubyGems: 3.0.3 - /usr/bin/gem
  Utilities:
    Make: 3.81 - /usr/bin/make
    GCC: 4.2.1 - /usr/bin/gcc
    Git: 2.21.0 - /usr/bin/git
    Clang: 1100.0.33.16 - /usr/bin/clang
    Subversion: 1.10.4 - /usr/bin/svn
  Servers:
    Apache: 2.4.41 - /usr/sbin/apachectl
  Virtualization:
    Docker: 19.03.5 - /usr/local/bin/docker
    VirtualBox: 6.0.14 - /usr/local/bin/vboxmanage
  SDKs:
    iOS SDK:
      Platforms: iOS 13.2, DriverKit 19.0, macOS 10.15, tvOS 13.2, watchOS 6.1
  IDEs:
    Nano: 2.0.6 - /usr/bin/nano
    VSCode: 1.41.1 - /usr/local/bin/code
    Vim: 8.1 - /usr/bin/vim
    Xcode: 11.3/11C29 - /usr/bin/xcodebuild
  Languages:
    Bash: 3.2.57 - /bin/bash
    Perl: 5.18.4 - /usr/bin/perl
    PHP: 7.3.9 - /usr/bin/php
    Python: 2.7.16 - /usr/bin/python
    Python3: 3.7.5 - /usr/local/bin/python3
    Ruby: 2.6.3 - /usr/bin/ruby
  Databases:
    SQLite: 3.28.0 - /usr/bin/sqlite3
  Browsers:
    Chrome: 79.0.3945.88
    Chrome Canary: 81.0.4020.0
    Firefox: 71.0
    Safari: 13.0.4

[jeysal]

I also think you may be overusing the coverage metric here, it can never tell you if you’re actually testing all relevant cases on its own. Code reviews are still required so that a human can spot at the usage of classnames that this piece of code requires a test case for “has the class” and one for “does not have the class” 😃

[github-actions[bot]]

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