QUESTION: dependency injection for unit tests

[kpeters-cbsi]

So how do you do dependency injection for testing with this framework? Say I have a function, listThings, implemented like so:

import type { Props } from '@exobase/core';
import makeStorageService, {
  StorageService,
} from '../storage-service';
import { useService } from '@exobase/hooks';
import _ from 'radash';
import config from '../config';

interface Args {
  listThingsArgs: any;
}

interface Services {
  storage: StorageService;
}

type Response = Array<string>;

async function listThings({args, services}: Props<Args, Services>): Promise<Response> {
  return this.services.storage.listThings(args.listThingsArgs)
}

export default _.compose(
  useService<Services>({
    storage: await makeStorageService(config.storageService)
  }),
  listThings
);

(As I'm sure you can deduce, I lifted a lot of this pattern from your published endpoint code)

So two things to note here:

First, there's no framework code here. While this is intended to run in Lambda / API Gateway, my goal is to be able to compose the framework code from Exobase with my function code so that I can very easily port this to another framework if need be.

Second, I'm loading my config in the function definiiton for listThings. If I want to use a custom config for my tests, how am I supposed to inject that? Or should I just mock the call to makeStorageService?

[kpeters-cbsi]

Ah! I'm Doing It Wrong! What I need to do here is to abstract the function code into its own file and then compose it with useService in my framework code (e.g. Lambda).

So something like this:

import {
  StorageService,
} from '../storage-service';
import config from '../config';

interface Args {
  listThingsArgs: any;
}

interface Services {
  storage: StorageService;
}

type Response = Array<string>;

async function listThings({args, services}: {args: Args, services: Services}): Promise<Response> {
  return this.services.storage.listThings(args.listThingsArgs)
}

export default listThings;

And then in my endpoint Lambda:

import type { Props } from '@exobase/core';
import makeStorageService from '../storage-service';
import { useService, useCors } from '@exobase/hooks';
import { useLambda } from '@exobase/lambda'
import * as _ from 'radash';
import config from '../config';

export default _.compose(
  useLambda(),
  useCors(),
  useService<Services>({
    storage: StorageService
  }),
  ({args, services}: Props<Args, Services>) => listThings({args, services}) // I haven't tried this out, so I may be slightly off base here
)

[kpeters-cbsi]

Leaving this open in case @rayepps or anyone else wants to comment further

[sodiray]

Hey @kpeters-cbsi thanks for bringing this up! So the way I do it is I keep it all in one file, I just export the endpoint function. In your first example, I would just add export to listThings so I can import it in my unit test.