Concrete reader monad over Matchers

Its MonadAWS instance can be used in tests where you don't have or want your own test-app transformer:

import Amazonka.S3
import Control.Monad.AWS

spec :: Spec
spec = do
  describe "someAction" $ do
    it "works" $ do
      let matcher = SendMatcher (const True) -- match all calls
           $ newListBucketsResponse          -- return no buckets
           & listBucketsResponse_buckets ?~ []

      names <- runMockT $ withMatcher matcher $ someAction
      names shouldBe []

someAction :: (MonadIO m, MonadAWS) m => m [BucketName]
someAction = do
  resp <- send newListBuckets
  pure
    $ maybe [] (map (^. bucket_name))
    $ resp ^. listBucketsResponse_buckets