Unit tests for GraphQLClient

[jackdclark]

Part of #9

Add test coverage for GraphQLClient

  GraphQLClient
    when instantiated
      ✓ throws if no url provided (10ms)
      ✓ throws if fetch is not a function (1ms)
      ✓ throws if fetch is not present or polyfilled (1ms)
      ✓ assigns config.cache to an instance property
      ✓ assigns config.headers to an instance property
      ✓ assigns config.ssrMode to an instance property
      ✓ assigns config.url to an instance property (1ms)
      ✓ assigns config.fetch to an instance property
      ✓ assigns config.fetchOptions to an instance property
      ✓ assigns config.logErrors to an instance property (1ms)
      ✓ assigns config.onError to an instance property
    setHeader
      ✓ sets the key to the value (1ms)
    setHeaders
      ✓ replaces all headers
    logErrorResult
      ✓ calls onError if present (3ms)
      ✓ logs a fetchError (2ms)
      ✓ logs an httpError
      ✓ logs all graphQLErrors (1ms)
    generateResult
      ✓ shows as errored if there are graphQL errors (1ms)
      ✓ shows as errored if there is a fetch error
      ✓ shows as errored if there is an http error
      ✓ returns the errors & data (1ms)
    getCacheKey
      ✓ returns a cache key
    request
      ✓ sends the request to the configured url (3ms)
      ✓ applies the configured headers
      ✓ sends the provided operation query, variables and name (1ms)
      ✓ handles & returns fetch errors (1ms)
      ✓ handles & returns http errors (1ms)
      ✓ returns valid responses
      ✓ returns graphql errors (1ms)
      ✓ will use a configured fetch implementation

[bmullan91]

LGTM - Fantastic start @jackdclark 👍

[bmullan91]

Minor: logErrors should be a Boolean

[bmullan91]

Minor: Sometimes it's useful to set actual and expected explicitly, making it a bit clearer to understand whats being tested:

const actual = fetch.mock.calls[0][0]
const expected = validConfig.url
expect(actual).toBe(expected)

[bmullan91]