Add utility for testing components that use GraphQlClient

[xenoterracide]

We're actively building a lot of code to integrate existing microservices into other services that are moving to a graphql interface. For now our services will remain REST. our services are "client only". What I'm looking for is an option akin to spring core's RestClientTest, where I can very quickly stub our limited responses with static responses. No idea for API at this time.

[rstoyanchev]

I'm not sure what RestClientTester is, but it sounds like MockRestServiceServer or based on it. There isn't anything exactly like that. However, you can use the same (i.e. MockRestServiceServer via RestClient/RestTemplate) to return canned GraphQL responses. It's just HTTP and doesn't necessarily need special handling, especially with canned responses.

You could also consider ExecutionGraphQlServiceTester, essentially GraphQlTester without a transport, and calling the GraphQL layer directly. You could add a little extra support around it to make it more convenient, like the MockExecutionGraphQlService that we use for own testing, for example here.

[xenoterracide]

google in it's infinite wisdom is having problems locating the reference/example documentation to

https://docs.spring.io/spring-boot/api/java/org/springframework/boot/test/autoconfigure/web/client/RestClientTest.html

baeldung has some though

https://www.baeldung.com/restclienttest-in-spring-boot

[bclozel]

I guess we're mixing things a bit here: what we'd like to test and how we'd like to test it, what Spring GraphQL can do to help and if/how Spring Boot can provide a test slice for this case.

I think that reproducing @RestClientTest with a MockRestServiceServer HTTP setup is not buying us much and can be done already today. Maybe considering a MockExecutionGraphQlService that plugs into a testing GraphQlTransport would work. The main problem is that we have specialized interfaces like HttpSyncGraphQlClient and that we promote specific static factory methods to create those using RestClient or WebClient. Components under test would probably need to have dedicated constructors accepting GraphQlTransport as well, but I think that if we provide a high-level testing utility this should still be a better solution.