Vue Test Utils

Slots

Vue Test Utils provides some useful features for testing components using slots.

A Simple Example

You might have a generic <layout> component that uses a default slot to render some content. For example:

const Layout = {
  template: `
    <div>
      <h1>Welcome!</h1>
      <main>
        <slot />
      </main>
      <footer>
        Thanks for visiting.
      </footer>
    </div>
  `
}

You might want to write a test to ensure the default slot content is rendered. VTU provides the slots mounting option for this purpose:

test('layout default slot', () => {
  const wrapper = mount(Layout, {
    slots: {
      default: 'Main Content'
    }
  })

  expect(wrapper.html()).toContain('Main Content')
})

It passes! In this example, we are passing some text content to the default slot. If you want to be even more specific, and verify the default slot content is rendered inside <main>, you could change the assertion:

test('layout default slot', () => {
  const wrapper = mount(Layout, {
    slots: {
      default: 'Main Content'
    }
  })

  expect(wrapper.find('main').text()).toContain('Main Content')
})

Named Slots

You may have more complex <layout> component with some named slots. For example:

const Layout = {
  template: `
    <div>
      <header>
        <slot name="header" />
      </header>

      <main>
        <slot name="main" />
      </main>
      <footer>
        <slot name="footer" />
      </footer>
    </div>
  `
}

VTU also supports this. You can write a test as follows. Note that in this example we are passing HTML instead of text content to the slots.

test('layout full page layout', () => {
  const wrapper = mount(Layout, {
    slots: {
      header: '<div>Header</div>',
      main: '<div>Main Content</div>',
      footer: '<div>Footer</div>'
    }
  })

  expect(wrapper.html()).toContain('<div>Header</div>')
  expect(wrapper.html()).toContain('<div>Main Content</div>')
  expect(wrapper.html()).toContain('<div>Footer</div>')
})

Multiple Slots

You can pass an array of slots, too:

test('layout full page layout', () => {
  const wrapper = mount(Layout, {
    slots: {
      default: [
        '<div id="one">One</div>',
        '<div id="two">Two</div>'
      ]
    }
  })

  expect(wrapper.find('#one').exists()).toBe(true)
  expect(wrapper.find('#two').exists()).toBe(true)
})

Advanced Usage

You can also pass a render function, an object with template or even an SFC imported from a vue file to a slot mounting option:

import { h } from 'vue'
import Header from './Header.vue'

test('layout full page layout', () => {
  const wrapper = mount(Layout, {
    slots: {
      header: Header
      main: h('div', 'Main Content'),
      sidebar: { template: '<div>Sidebar</div>' },
      footer: '<div>Footer</div>',
    }
  })

  expect(wrapper.html()).toContain('<div>Header</div>')
  expect(wrapper.html()).toContain('<div>Main Content</div>')
  expect(wrapper.html()).toContain('<div>Footer</div>')
})

Refer to the tests for more examples and use cases.

Scoped Slots

Scoped slots and bindings are also supported.

const ComponentWithSlots = {
  template: `
    <div class="scoped">
      <slot name="scoped" v-bind="{ msg }" />
    </div>
  `,
  data() {
    return {
      msg: 'world'
    }
  }
}

test('scoped slots', () => {
  const wrapper = mount(ComponentWithSlots, {
    slots: {
      scoped: `<template #scoped="scope">
        Hello {{ scope.msg }}
        </template>
      `
    }
  })

  expect(wrapper.html()).toContain('Hello world')
})

When using string templates for slot content, if not explicitly defined using a wrapping <template #scoped="scopeVar"> tag, slot scope becomes available as a params object when the slot is evaluated.

test('scoped slots', () => {
  const wrapper = mount(ComponentWithSlots, {
    slots: {
      scoped: `Hello {{ params.msg }}` // no wrapping template tag provided, slot scope exposed as "params"
    }
  })

  expect(wrapper.html()).toContain('Hello world')
})

## Conclusion

- Use the `slots` mounting option to test components using `<slot>` are rendering content correctly.
- Content can either be a string, a render function or an imported SFC.
- Use `default` for the default slot, and the correct name for a named slots.
- scoped slots and the `#` shorthand is also supported.