Refactor src/events/scraper/load-cache/index.js

[jzohrab]

Change API to take the loader, and add tests. Passing in the loader object rather than a boolean should clarify flow. Can also standardize on throwing instead of returning false,

• How will this make life better?

Clearer code path

• How big is this change (small/med/large/really large)?

Small

• How complicated is it?

Medium. Code exists and works, but IMO is hard to follow.

• What's the test plan?

Dependency inject for unit testing to simulate cache fall through.

e.g:

async function load(params, loader) { ... }

async function loadCache(params) {
  if (isLocal) {
    try {
      let result = await load(params, localLoader)
      return result
    }
    catch {
      ... cache miss
    }
  }

  // S3 load
  try {
    let result = await load(params, S3Loader)
    return result
  }
  catch {
    ... failure
  }
}

[jzohrab]

Opened PR #232 for this. I started adding tests but due to the multiple execution paths and exit conditions it became messy -- I'd still like to get those tests in but this PR is a good start.