added meaningful error for variable mismatch and caught a number of f…

[chanceeakin]

…laky tests

Description:

MockedProvider is incredibly useful, but its error messages are terse and most fall under the 'no more mocked responses.' Most often, this error is because of a variable mismatch. I added an explicit error for variables mismatches, as well as found some flaky tests relying on a lack of meaningful errors.

Checklist:

• If this PR is a new feature, please reference an issue where a consensus about the design was reached (not necessary for small changes)
• Make sure all of the significant new logic is covered by tests
• If this was a change that affects the external API used in GitHunt-React, update GitHunt-React and post a link to the PR in the discussion.

[apollo-cla]

@chanceeakin: Thank you for submitting a pull request! Before we can merge it, you'll need to sign the Apollo Contributor License Agreement here: https://contribute.apollographql.com/

[chanceeakin]

Hey, this PR is currently failing; uncovered some flaky tests with the addition of the error. Marked them in the PR and would love some help with resolving them.😄

For reference: #3481.

[piotrd]

Any updates on this one by chance?

[chanceeakin]

@piotrd Not that I've seen. 🤷‍♂️Wanna give it a bump?