Error handling within MockedProvider

[NickTomlin]

The current createApolloErrorProvider approach has a separate "throw an error for all requests". This is useful for inspecting the behavior of errors on initial load, but breaks down for me when I have a view that may render some data with a query (like a list of items) and execute another query/mutation on that data.

I'd prefer to be able to control the error handling within my custom resolvers. I've taken a crack at it here. Here is a snippet of usage:

<MockedProvider
  customResolvers={{
    Query: () => ({
      todo: (_obj: any, args: any) => {
        console.log(args.id)
        throw new Error('Boom');
      },
      todos: () => [
        {
          text: 'Success',
        },
      ],
    }),
  }}
>

This would allow a todos query to execute, and then throw an error when todo(id: ID) is executed. Optionally, a resolver can inspect its arguments and conditionally throw an error. This would allow for a more natural way of handling complex error scenarios.

[benawad]

I like that approach, I'd be happy to merge a pr for that.

[sarfata]

@NickTomlin I could use this too. Any reason you have not made a PR yet?

If you do not have time, I could take your fork, check that it builds with recent changes and make the PR. PR ready to merge :)

[NickTomlin]

@sarfata thanks for merging! My wife and I recently welcomed a child so I haven't had any time to focus on this 😄

One issue that I did encounter (which was why I hadn't merged my initial work) is that errors thrown in mutation resolvers do not work as expected. By default, they caught by the error handler and also thrown by Apollo. Here's a reproduction (npm t should result in a failing test). More details in apollographql/react-apollo#2614

The "fix" is to either specify an onError policy on the Mutation (which is ugly, because you shouldn't have to do this just for tests) or to set a mutation error policy of all on the client:

const client = new ApolloClient({
  defaultOptions: {
    mutate: {
      errorPolicy: 'all'
    }
  },
});

If you add the defaultOptions snippet to createApolloMockedProvider the test in my reproduction branch should work. It feels a little weird to default the error policy for all the mocked providers. If there's not a better fix we could allow passing a defaultOptions object to createApolloMockedProvider which could override that behavior.

[sarfata]

Hey @NickTomlin Congrats on the baby! Sorry for the delay here. Just wanted to acknowledge and say that I will get around to doing that and pushing a new PR. Thanks for pointing this out.

[netweng]

i have the problem when throw error in mutation, can this be fixed or i need to fork the repo and add the defaultOptions for errorPolicy.

[benawad]

@netweng happy to merge a pr

[lorensr]

Here's a problem I'm having with this feature: #31