feat(core): allow running adhoc functions in tests

[xavdid]

Addresses #16.

see also: PDE-2539

Todo

• verify that TS works nicely
• write unit tests

Testing

1. With this PR cloned locally, run yarn link in the core directory
2. elsewhere, run zapier init ad-hoc-test -t custom-auth
3. run cd ad-hoc-test && yarn && yarn link zapier-platform-core

Now, appTester can be fed ad-hoc functions. Try the following test:

/* globals describe, it, expect */

const zapier = require("zapier-platform-core");

const App = require("../index");
const appTester = zapier.createAppTester(App);

describe("custom auth", () => {
  it("passes authentication and returns json", async () => {
    const bundle = {
      authData: {
        apiKey: "secret",
      },
    };

    const response = await appTester(
      (z, bundle) =>
        z.request({ url: "https://auth-json-server.zapier-staging.com/me" }),
      bundle    
    );
    expect(response.data).toHaveProperty("username");
  });
});

It's a simple test, but it proves a point: a test function can use z.request and take advantage of middleware.

[xavdid]

@eliangcs this isn't ready for an actual review yet, but I figured it would be worth getting some early eyes just in case there's a reason we shouldn't pursue this.

[eliangcs]

@xavdid this is cool! But I wonder what prevents developers from doing this injection inside their code. In #16, @Lardpower mentioned they could inject the function in the test code:

let App = require('../../index');

// include any custom functions in any custom App field like "lib"
App.lib = {
    user: require('./lib/user.js')
}

...

// use it later during the test
appTester(App.lib.user.get).then(response => {});

I'm probably missing something. Does the above code have any problems?

[xavdid]

That's a valid workaround, but it's sort of an antipattern to tell users to add invalid properties to their app. If it's behavior we want to support, then being able to call functions inline (pre-defined or otherwise) feels better. Feels more "above the board".

Does that make sense? Should I go ahead with finishing this PR?

[eliangcs]

@xavdid the feature request makes sense to me, but I don't think the adHoc flag is necessary. Could we make appTester automatically inject the function if it doesn't exist in the app definition? Something like:

    let method;
    try {
      method = resolveMethodPath(appRaw, methodOrFunc);
    } catch (err) {
      // We may need to let resolveMethodPath throw different error types to do this
      if (e instanceof MethodNotfound) {
        appRaw._testRequest = (z, bundle) => methodOrFunc(z, bundle);
        method = resolveMethodPath(appRaw, methodOrFunc);
      } else {
        throw err;
      }
    }

What do you think?

[xavdid]

Sure, makes sense. I did it without a property in 67b48f6. We'll run any function we get, but it correctly throws errors if you give an object (or other allowed type) that isn't found.

[eliangcs]

@xavdid looking good! Let me know once this PR is ready for review.

[xavdid]

Ok, this is ready! added tests, docs, and cleaned up resolveMethodPath while I Was in there.

[eliangcs]

Thanks for the good test coverage! I only have a suggestion on the docs.