N
Nuxt•3w ago
dmarr

mocking useI18n with nuxt i18n module

What previously worked within my tests to handle mocking useI18n calls no longer does. I get the error Must be called at the top of a setup function How frustrating!
3 Replies
kapa.ai
kapa.ai•3w ago
Hi @dmarr. I'm kapa.ai, your friendly support bot. I will try to answer your question by searching through the knowledge base. :wave: ---------------------- I understand your frustration with mocking useI18n in your Nuxt tests. This is a common issue when testing components that use the i18n module. The error "Must be called at the top of a setup function" occurs because composables like useI18n need to be called within a component's setup context. When you're writing tests, this context isn't automatically available. Based on the knowledge sources, there are a few approaches to mock the useI18n function in your tests: Using mockNuxtImport The recommended approach is to use mockNuxtImport from @nuxt/test-utils/runtime: 
import { mockNuxtImport } from '@nuxt/test-utils/runtime'

mockNuxtImport('useI18n', () => {
  return () => ({
    t: (key) => key, // Simple mock that returns the key
    locale: { value: 'en' },
    setLocale: vi.fn()
    // Add other properties/methods you need
  })
})

// your tests here
import { mockNuxtImport } from '@nuxt/test-utils/runtime'

mockNuxtImport('useI18n', () => {
  return () => ({
    t: (key) => key, // Simple mock that returns the key
    locale: { value: 'en' },
    setLocale: vi.fn()
    // Add other properties/methods you need
  })
})

// your tests here
This approach is documented in the Nuxt Testing documentation and is the most straightforward way to mock Nuxt's auto-imports. For Different Implementations Between Tests If you need different implementations between tests, you can use vi.hoisted: 
import { vi } from 'vitest'
import { mockNuxtImport } from '@nuxt/test-utils/runtime'

const { useI18nMock } = vi.hoisted(() => {
  return {
    useI18nMock: vi.fn(() => ({
      t: (key) => key,
      locale: { value: 'en' },
      setLocale: vi.fn()
    }))
  }
})

mockNuxtImport('useI18n', () => {
  return useI18nMock
})

// Then, inside a test you can change the implementation
useI18nMock.mockImplementation(() => ({
  t: (key) => `translated-${key}`,
  locale: { value: 'fr' },
  setLocale: vi.fn()
}))
import { vi } from 'vitest'
import { mockNuxtImport } from '@nuxt/test-utils/runtime'

const { useI18nMock } = vi.hoisted(() => {
  return {
    useI18nMock: vi.fn(() => ({
      t: (key) => key,
      locale: { value: 'en' },
      setLocale: vi.fn()
    }))
  }
})

mockNuxtImport('useI18n', () => {
  return useI18nMock
})

// Then, inside a test you can change the implementation
useI18nMock.mockImplementation(() => ({
  t: (key) => `translated-${key}`,
  locale: { value: 'fr' },
  setLocale: vi.fn()
}))
Remember that recent changes in Nuxt might have affected how mocking works. The knowledge sources mention a PR (#31295) that changed how mocked exports work, which could be related to your issue. Make sure you're using the latest version of @nuxt/test-utils and check if there are any specific requirements for your version of Nuxt. Let me know if you need more specific help with your testing setup! ---------------------- Note: you can ask me a follow up question by @ mentioning me again :speech_balloon: ----------------------
kapa.ai
kapa.ai•3w ago
<@139883350096740354> Kapa.ai is still learning and improving, please let me know how I did by reacting below.
dmarr
dmarrOP•3w ago
Also on the docs for mockNuxtImport: https://nuxt.com/docs/getting-started/testing#mocknuxtimport The suggestion: 
import { vi } from 'vitest'
import { mockNuxtImport } from '@nuxt/test-utils/runtime'

const { useStorageMock } = vi.hoisted(() => {
  return {
    useStorageMock: vi.fn(() => {
      return { value: 'mocked storage'}
    })
  }
})

mockNuxtImport('useStorage', () => {
  return useStorageMock
})

// Then, inside a test
useStorageMock.mockImplementation(() => {
  return { value: 'something else' }
})
import { vi } from 'vitest'
import { mockNuxtImport } from '@nuxt/test-utils/runtime'

const { useStorageMock } = vi.hoisted(() => {
  return {
    useStorageMock: vi.fn(() => {
      return { value: 'mocked storage'}
    })
  }
})

mockNuxtImport('useStorage', () => {
  return useStorageMock
})

// Then, inside a test
useStorageMock.mockImplementation(() => {
  return { value: 'something else' }
})
if i wanted to pu those parts in the vitest global setup, how would I get access to useStorageMock?
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