How to use Gatsby cache with sourceNodes api

I am trying to set some cache using sourceNodes api and can't seem to get the cache to persist. I always get No Data for some reason. I looked inside of .cache/caches/[mypluginname]/[cacheFileHere] and it seems that on every run of gatsby develop it gets removed/recreated instead of just using the cache. Any ideas?

Here is my code:

exports.onSourceNodes  = async (props) => {
  const { cache } = props
  const cacheKey = `cooltestkey`
  const testData = { fig: "newton" }

  let data = await cache.get(cacheKey)

  if(!data) {
    console.log(`I don't exist`)
    await cache.set(cacheKey, testData)
  } else {
    console.log(`Hello I exist`)
  }
}