MockedProvider gives incorrect error message with undefined variables

Intended outcome:

MockedProvider error message correctly describes GraphQL request missing a mock when no matching mock present

Actual outcome:

No more mocked responses for the query: query GetIssues($a: ID, $b: ID, $c: String!, $d: String!) {
      getIssues(a: $a, b $b, c: $c, d: $d) {
        id
        name
      }
    }
    , variables: {"a":"123","c":"456","d":"789"}

Note that the query I am sending actually has b: undefined in the variables, and that’s why the mock (which did not include b in the variables) did not match, but MockedProvider did not tell me this.

How to reproduce the issue:

Set up a mock for a query that takes an optional variable, pass undefined to it in your code, but omit it from variables in your mock. It will fail to match, but the error message will not mention it.

Versions

  System:
    OS: Linux 5.3 Ubuntu 19.10 (Eoan Ermine)
  Binaries:
    Node: 13.8.0 - ~/n/bin/node
    Yarn: 1.22.0 - ~/duboce-labs/pganalyze/node_modules/.bin/yarn
    npm: 6.14.4 - ~/n/bin/npm
  Browsers:
    Chrome: 84.0.4147.89
    Firefox: 78.0.2
  npmPackages:
    @apollo/client: ^3.0.2 => 3.0.2 
    apollo: ^2.23.0 => 2.23.0 
  npmGlobalPackages:
    apollo: 2.18.3

[vith]

I don’t think #7108 fixed this.

I’ve offered a fix for the error message, and some failing tests for the mock matching behavior itself in #8285

Can we reopen?

[benjamn]

To be completely honest with you, we did not get around to improving our testing/mocking utilities in AC3, but they are badly in need of an update, and this is a great example of a shortcoming in how the mocking utilities match queries/variables. Thanks for opening this issue!