The [tests](https://github.com/jml/graphql-api/blob/2b64b65175a315cc8a5247aa519793f40d8b6058/tests/EndToEndTests.hs#L240-L290) use a variable map, but the variable is not passed as a parameter to a handler. Instead, [the handler already has the variable hard coded](https://github.com/jml/graphql-api/blob/2b64b65175a315cc8a5247aa519793f40d8b6058/tests/EndToEndTests.hs#L241). How can a variable [from the variable map](https://github.com/jml/graphql-api/blob/2b64b65175a315cc8a5247aa519793f40d8b6058/tests/EndToEndTests.hs#L278-L279) be passed as a value to the handler?