wildcard-mock-link

WildcardMockLink is a replacement for MockLink which can:

• Match requests with arbitrary variables.
• Provide mocks that match more than one request.
• Mock subscriptions and send subscription responses after setting up the MockedProvider in a test via method calls.
• Grab the mutation/query/subscription requests for use in test assertions.

Documentation

Wildcard queries

The MockLink provided with apollo requires the variables for every matching query to be specified ahead of time. In certain circumstances this is not convenient, i.e. using the MockedProvider in storybook stories. WildcardMockLink allows mocks to be specified that match a query with any variables, and these mocks can be configured to match more than once.

import { act } from '@testing-library/react'

const CAT_QUALITIES_QUERY = gql`
  query ($catName: String!) {
    qualities(cats: $catName) {
      loveliness
    }
  }
`

const link = new WildcardMockLink(
  [
    {
      request: {
        query: CAT_QUALITIES_QUERY,
        variables: MATCH_ANY_PARAMETERS,
      },
      result: { data },
      nMatches: 2,
    },
  ],
  { addTypename: true, act },
)

return (
  <MockedProvider link={link}>
    <MyCatComponent />
  </MockedProvider>
)

The above mocked provider will match two requests for CAT_QUALITIES_QUERY no matter what the variables are. Here nMatches is used to restrict the mock to the first two requests that match, when nMatches is omitted the mock will match one request. Number.POSITIVE_INFINITY can be used to allow an inifinite number of matchs.

The instantiation of WildcardMockLink also shows the options, addTypename which works the same as apollo's MockLink and act which can be used to ensure all operations that emit data to components are wrapped in an act function. suppressMissingMockWarnings will disable the console.warn about missing mocks, defaults to false.

Asserting against the latest request/mutation/subscription.

The following returns true if the last query matches CAT_QUALITIES_QUERY.

link.lastQueryMatches(CAT_QUALITIES_QUERY)

There are also lastMutationMatches and lastSubscriptionMatches. The arrays queries, mutations and subscriptions contain all of the corresponding requests.

Waiting for responses to return data

These methods can be used to ensure updates don't happen outside of act.

await link.waitForLastResponse()

This waits for the last response to complete.

await link.waitForAllResponses()

This waits for all pending responses to complete.

await link.waitForAllResponsesRecursively()

This can be used when a component makes a new request based on data received from another response. It waits until there are no more pending responses.

Testing components with mock data

This library provides a utility function withApolloMocks which can be used to created a component tree with access to mocked data. It returns the react element at the head of the component tree and a WildcardMockLink object and can be used in conjunction with the functionality mentioned above to create a test like this:

import { useQuery } from '@apollo/client'
import { render, act } from '@testing-library/react'
import gql from 'graphql-tag'
import React, { FC } from 'react'
import {
  MATCH_ANY_PARAMETERS,
  hookWrapperWithApolloMocks,
} from 'wildcard-mock-link'

const CAT_QUALITIES_QUERY = gql`
  query ($catName: String!) {
    qualities(cats: $catName) {
      loveliness
    }
  }
`

it('can be used to mock data for a component tree', async () => {
  const data = {
    qualities: {
      __typename: 'Qualities',
      loveliness: 'very',
    },
  }

  const { element, link } = withApolloMocks(
    () => <MyCatComponent catName="mr bad actor face" />,
    [
      {
        request: {
          query: CAT_QUALITIES_QUERY,
          variables: MATCH_ANY_PARAMETERS,
        },
        result: { data },
      },
    ],
  )
  const { getByRole } = render(element)
  await link.waitForLastResponse()

  expect(link.lastQueryMatches(CAT_QUALITIES_QUERY)).toBeTruthy()
  expect(link.lastQuery?.variables).toEqual({ catName: 'mr bad actor face' })
  const mainContent = getByRole('main')
  expect(mainContent?.textContent).toEqual('Loveliness: very')
})

Testing hooks with mock data

This library provides a utility function hookWrapperWithApolloMocks for creating a wrapper object which can be used with @testing-library/react-hooks. It returns a WildcardMockLink and a wrapper and can be used in conjunction with the functionality mentioned above to create a test like this:

import { useQuery } from '@apollo/client'
import { renderHook, act as actHook } from '@testing-library/react-hooks'
import gql from 'graphql-tag'
import {
  MATCH_ANY_PARAMETERS,
  hookWrapperWithApolloMocks,
} from 'wildcard-mock-link'

const CAT_QUALITIES_QUERY = gql`
  query ($catName: String!) {
    qualities(cats: $catName) {
      loveliness
    }
  }
`

it('can be used to mock data for a hook', async () => {
  const useQueryOnce = (catName: string) => {
    const { data } = useQuery(CAT_QUALITIES_QUERY, { variables: { catName } })
    return data
  }

  const data = {
    qualities: {
      __typename: 'Qualities',
      loveliness: 'very',
    },
  }
  const { wrapper, link } = hookWrapperWithApolloMocks([
    {
      request: {
        query: CAT_QUALITIES_QUERY,
        variables: MATCH_ANY_PARAMETERS,
      },
      result: { data },
    },
  ])
  const { result } = renderHook(() => useQueryOnce('tortand'), { wrapper })
  await link.waitForLastResponse()
  expect(link.lastQueryMatches(CAT_QUALITIES_QUERY)).toBeTruthy()
  expect(link.lastQuery!.variables).toEqual({ catName: 'tortand' })
  expect(result.current).toEqual(data)
})

Testing subscriptions with multiple responses

The WildcardMockLink provides a way to push new responses out to subscriptions. This can be used during tests to make it easier to test how components respond to subscription updates. The sendWildcardSubscriptionResult method can be used to send a new response which matches a wildcard mock, otherwise sendSubscriptionResult can be used. Here is an example:

import { useQuery } from '@apollo/client'
import { waitFor } from '@testing-library/react'
import { renderHook, act as actHook } from '@testing-library/react-hooks'
import gql from 'graphql-tag'
import {
  MATCH_ANY_PARAMETERS,
  hookWrapperWithApolloMocks,
} from 'wildcard-mock-link'

const MISCHIEF_SUBSCRIPTION = gql`
  subscription ($catName: String!) {
    actsOfMischief(cats: $catName) {
      description
      severity
    }
  }
`

it('can push updates using the API', async () => {
  const useActsOfMischief = (catName: string) => {
    const { data } = useSubscription(MISCHIEF_SUBSCRIPTION, {
      variables: { catName },
    })
    return data
  }

  const initialData = {
    actsOfMischief: {
      __typename: 'ActsOfMischief',
      description: 'did not stay away from my bins',
      severity: 'extreme',
    },
  }
  const { wrapper, link } = hookWrapperWithApolloMocks(
    [
      {
        request: {
          query: MISCHIEF_SUBSCRIPTION,
          variables: MATCH_ANY_PARAMETERS,
        },
        result: { data: initialData },
      },
    ],
    undefined,
    { act: actHook },
  )
  const rendered = renderHook(() => useActsOfMischief('la don'), { wrapper })
  expect(link.lastSubscriptionMatches(MISCHIEF_SUBSCRIPTION)).toBeTruthy()
  expect(link.lastSubscription?.variables).toEqual({ catName: 'la don' })

  await waitFor(() => {
    expect(rendered.result.current).toEqual(initialData)
  })

  const updateData = {
    actsOfMischief: {
      __typename: 'ActsOfMischief',
      description: 'pushed that button',
      severity: 'mild',
    },
  }
  link.sendWildcardSubscriptionResult(MISCHIEF_SUBSCRIPTION, {
    data: updateData,
  })
  await waitFor(() => {
    expect(rendered.result.current).toEqual(updateData)
  })
})