Add some comments

__tests__/helpers.ts

@@ -20,15 +20,18 @@ export const removeDanglingUpdaterContainers = async (): Promise<void> => {
 }
 
 export const runFakeDependabotApi = async (port: number): Promise<Function> => {
-  const server = spawn(`${path.join(__dirname, 'server/server.js')}`, [
+  const server = spawn('node', [
+    `${path.join(__dirname, 'server/server.js')}`,
     `${port}`
   ])
+
   server.stdout.on('data', (data: any) => {
     console.log(`json-server log: ${data}`) // eslint-disable-line no-console
   })
   server.stderr.on('data', (data: any) => {
     console.error(`json-server error: ${data}`) // eslint-disable-line no-console
   })
+
   await waitPort({port})
 
   return (): void => {

__tests__/server/server.js

@@ -1,15 +1,20 @@
-#!/usr/bin/env node
-
 const jsonServer = require('json-server')
 const path = require('path')
 const fs = require('fs')
 const server = jsonServer.create()
 const db = JSON.parse(fs.readFileSync(path.join(__dirname, 'db.json')))
 const router = jsonServer.router(db)
 const middlewares = jsonServer.defaults()
-
 const SERVER_PORT = process.argv.slice(2)[0] || 9000
 
+// Sets up a fake dependabot-api using json-server
+//
+// Test it locally by running this script directly:
+// $ node __tests__/server/server.js
+// Running on http://localhost:9000
+//
+// Verify it works: curl http://localhost:9000/update_jobs/1/details
+
 // NOTE: Serialise the response like dependabot-api
 router.render = (_, res) => {
   const id = res.locals.data.id