Jest Uncovered Lines - How do I test these lines..?

Question

I'm using Jest with the coverage option on and I'm getting:

--------------------------|----------|----------|----------|----------|----------------|
File                      |  % Stmts | % Branch |  % Funcs |  % Lines |Uncovered Lines |
--------------------------|----------|----------|----------|----------|----------------|
progress-bar.js           |      100 |       75 |      100 |      100 |             17 |
--------------------------|----------|----------|----------|----------|----------------|

So I have 17 uncovered lines, but I'm not sure how to cover them.

progress-bar.js

import ProgressBar from 'progress'
import isNumber from 'lodash/isNumber'
import config from '../../config/global'

function progressBar (total) {
  if (!isNumber(total)) throw new Error(`progressBar() 'total' arg is not a number.`)

  const barCfg = config.progressBar

  const tokens = `${barCfg.bar} ${barCfg.info}`

  const options = {
    width: barCfg.width,
    total: total || 1,
    complete: barCfg.complete,
    incomplete: barCfg.incomplete
  }

  const bar = new ProgressBar(tokens, options)

  bar.render()

  return bar
}

export default progressBar

progress-bar.test.js

import ProgressBar from 'progress'
import progressBar from './progress-bar'

describe('progressBar()', () => {
  test('returns instanceof ProgressBar', () => {
    const actual = progressBar(5) instanceof ProgressBar
    const expected = true
    expect(actual).toBe(expected)
  })

  test('throw error if arg "total" is not a number', () => {
    expect(() => { progressBar('moo') }).toThrow()
    expect(() => { progressBar(null) }).toThrow()
  })

  test('progress bar progress/ticking', () => {
    const bar = progressBar(5)
    expect(bar.total).toBe(5)
    expect(bar.curr).toBe(0)
    bar.tick()
    expect(bar.curr).toBe(1)
    bar.tick()
    expect(bar.curr).toBe(2)
    bar.tick()
    expect(bar.curr).toBe(3)
    bar.tick()
    expect(bar.curr).toBe(4)
    bar.tick()
    expect(bar.curr).toBe(5)
    expect(bar.complete).toBe(true)
  })
})

So I'm testing the argument and return values.

How do I fully test this function, including the 17 lines..?

Answer 1

Ok, I am now sitting in the corner with my dunce hat on.

Found this: https://github.com/istanbuljs/nyc/issues/35#issuecomment-121008298

Uncovered Lines = 17 isn't a count of the uncovered lines, it's a list with only one value, that is, line 17: total: total || 1,.

Fixed with...

test('passing zero forces the default total of 1', () => {
  const bar = progressBar(0)
  expect(bar.total).toBe(1)
})

Answer 2

If you know what line number is uncovered, but can't figure out why the line is uncovered:

If the 'uncovered lines' are in yellow, it means they're partially covered. You can find out what specific attributes are not covered by producing an HTML report of the coverage:

npx jest --coverage --coverageDirectory='coverage'

Then open coverage/lcov-report/index.html which will show the specific codepaths which are untested

In my case, a function had a default arg foo = false, it was being tested with different values for the arg, but the default wasn't being tested so it was showing up as yellow.