app_spec.rb

# ...      l
      let(:s3_resource) { instance_double(Aws::S3::Resource, bucket: bucket) }
      let(:bucket) { instance_double(Aws::S3::Bucket) }
      let(:object) { instance_double(Aws::S3::Object, etag: 'sample_etag', key: file_key, size: 1_234) }

      before(:each) do
        ENV['S3_BUCKET'] = test_bucket_name
        allow(Aws::S3::Resource).to receive(:new).and_return(s3_resource)
        allow(s3_resource).to receive(:bucket).with(test_bucket_name).and_return(bucket)
        allow(bucket).to receive(:object).with(file_key).and_return(object)
        allow(object).to receive(:delete).and_return(true)
      end

      it { is_expected.to be true }
# ...