Utility module for black box testing

[jasonkuhrt]

What

• Support specification-based testing (aka. black box testing)

• Abstract the running of the app

• Abstract the running of multiple app instances

• API sketch (based on prior discussion)

   import { createTestContext } from "santa"
   
   const ctx = createTestContext()
   
   beforeAll(async () => {
     await ctx.app.server.start()
   })
   
   afterAll(async () => {
     await ctx.app.server.stop()
   })
   
   it('answers back', () => {
     expect(ctx.app.query(`
       query {
         foo {
           bar
         }
       }
     `)
   }).resolves.toMatchSnapshot()	

Why

• While exploring Website guide for testing #239 we discovered a few issues, including this one.
• We want to make it easy for users to test their santa app.

How

• We'll need to do random port finding, as there is a running app per test suite (file) and sharing a port would conflict

[jasonkuhrt]

CC @Weakky I sketched above that the server start/stop be an explicit part of the test context api. Thoughts? This would appear to allow context creation to be synchronous.

[jasonkuhrt]

Our approach is validated by how Spectrum.app tests.

https://github.com/withspectrum/spectrum/blob/alpha/docs/api/graphql/testing.md

Also, I don't think promises work with snapshots directly. That's what I encountered once and would explain the approach taken by Spectrum.app:

	return request(query).then(result => {
      // Use Jest snapshot testing for neater tests and easier diffs
      expect(result).toMatchSnapshot();
    });

[Weakky]

Shipped by #243