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Testing Vue.js Components with Jest

Mock External Module Dependencies

Explore how to mock external module dependencies in Vue.js tests using Jest. Learn to replace axios calls with mocks to test methods without making real HTTP requests. Understand how to check promise returns and update component state in your tests for robust unit testing.

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Testing Methods

What should we test in methods? That’s a question that we had when we started doing unit tests. Everything comes down to testing what that method does. This means that we need to avoid calls to any dependency; so, we’ll need to mock them.

Let’s add a submit event to the form in the Form.vue component that we created in the last chapter:

require('./check-versions')()

process.env.NODE_ENV = 'production'

var ora = require('ora')
var rm = require('rimraf')
var path = require('path')
var chalk = require('chalk')
var webpack = require('webpack')
var config = require('../config')
var webpackConfig = require('./webpack.prod.conf')

var spinner = ora('building for production...')
spinner.start()

rm(path.join(config.build.assetsRoot, config.build.assetsSubDirectory), err => {
  if (err) throw err
  webpack(webpackConfig, function (err, stats) {
    spinner.stop()
    if (err) throw err
    process.stdout.write(stats.toString({
      colors: true,
      modules: false,
      children: false,
      chunks: false,
      chunkModules: false
    }) + '\n\n')

    console.log(chalk.cyan('  Build complete.\n'))
    console.log(chalk.yellow(
      '  Tip: built files are meant to be served over an HTTP server.\n' +
      '  Opening index.html over file:// won\'t work.\n'
    ))
  })
})

The .prevent modifier is just a convenient way to call event.preventDefault() in order to prevent reloading the page. Now make some modifications to call an API and store the result, by adding a results array to the data and an onSubmit method:

require('./check-versions')()

process.env.NODE_ENV = 'production'

var ora = require('ora')
var rm = require('rimraf')
var path = require('path')
var chalk = require('chalk')
var webpack = require('webpack')
var config = require('../config')
var webpackConfig = require('./webpack.prod.conf')

var spinner = ora('building for production...')
spinner.start()

rm(path.join(config.build.assetsRoot, config.build.assetsSubDirectory), err => {
  if (err) throw err
  webpack(webpackConfig, function (err, stats) {
    spinner.stop()
    if (err) throw err
    process.stdout.write(stats.toString({
      colors: true,
      modules: false,
      children: false,
      chunks: false,
      chunkModules: false
    }) + '\n\n')

    console.log(chalk.cyan('  Build complete.\n'))
    console.log(chalk.yellow(
      '  Tip: built files are meant to be served over an HTTP server.\n' +
      '  Opening index.html over file:// won\'t work.\n'
    ))
  })
})

The ...