Description

This is a boilerplate project created by @vue/cli to demonstrate the broken coverage reporting when running Jest unit testing.

Steps to recreate this project.

system prerequisites: node 16.15.0, @vue/cli 5.0.4

Create a new project using @vue/cli

vue create testproject

select ‘Manually select features’ Select:

• Babel
• Linter / Formatter
• Unit Testing

Choose version of Vue.js: 2.x
Linter / formatter ESLint + Standard config
Lint on Save
Testing solution: Jest
config placement for Babel, ESLint, etc: In dedicated config files

wait for project to build...

cd testproject

in jest.config.js add collectCoverage: true

module.exports = {
  preset: '@vue/cli-plugin-unit-jest',
  collectCoverage: true
}

Add a simple method to src/components/HelloWorld.vue and save:

<script>
export default {
  name: 'HelloWorld',
  props: {
    msg: String
  },
  methods: {
    sum (a, b) {
      return a + b
    }
  }
}
</script>

Run the test suite:

yarn test:unit

Coverage report shows 100% code coverage despite there being no test for the sum method

 PASS  tests/unit/example.spec.js
  HelloWorld.vue
    ✓ renders props.msg when passed (39 ms)

----------------|---------|----------|---------|---------|-------------------
File            | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s 
----------------|---------|----------|---------|---------|-------------------
All files       |     100 |      100 |     100 |     100 |                   
 HelloWorld.vue |     100 |      100 |     100 |     100 |                   
----------------|---------|----------|---------|---------|-------------------
Test Suites: 1 passed, 1 total
Tests:       1 passed, 1 total
Snapshots:   0 total
Time:        2.58 s
Ran all test suites.
✨  Done in 8.58s.

Expected Result

This bug does not appear in Vue3 apps. This test in Vue3 yields the correct coverage report.

 PASS  tests/unit/example.spec.ts
  HelloWorld.vue
    ✓ renders props.msg when passed (58 ms)

----------------|---------|----------|---------|---------|-------------------
File            | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s 
----------------|---------|----------|---------|---------|-------------------
All files       |   66.66 |      100 |       0 |   66.66 |                   
 HelloWorld.vue |   66.66 |      100 |       0 |   66.66 | 45                
----------------|---------|----------|---------|---------|-------------------
Test Suites: 1 passed, 1 total
Tests:       1 passed, 1 total
Snapshots:   0 total
Time:        6.518 s
Ran all test suites.
✨  Done in 10.09s.

Below is the boilerplate Readme content from vue cli if you'd prefer to clone this repo instead of going through the setup steps above.

Project setup

yarn install

Compiles and hot-reloads for development

yarn serve

Compiles and minifies for production

yarn build

Run your unit tests

yarn test:unit

Lints and fixes files

yarn lint

Customize configuration

See Configuration Reference.