Can't mock nested field resolvers

[sunesimonsen]

Issue workflow progress

Progress of the issue based on the Contributor Workflow

• [x] 1. The issue provides a reproduction available on Github, Stackblitz or CodeSandbox

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  Please make sure the GraphQL Tools package versions under package.json matches yours.

• [x] 2. A failing test has been provided
• [ ] 3. A local solution has been provided
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Describe the bug

When mocking a nested root query, I can override any simple field, but overriding resolver fields doesn't work.

To Reproduce

Here is a test showing the problem

You can run the test in my fork, or just copy over the test.

Expected behavior

I expect returnStringArgument to have the value Overridden, but I get the default string value Hello World.

Environment:

• OS: OSX
• @graphql-tools/mock:
• NodeJS: v16.18.0

Additional context

I'm trying to fix a problem we are seeing in another tool graphql-fakester