function compareSnapshot(snapshotDir, outputFiles) {
  if (!fs.existsSync(snapshotDir) || fs.readdirSync(snapshotDir).length === 0) {
    throw new Error(`Did not find any stored snapshot at: ${snapshotDir}`);
  }

  checkFilesInDirectory(snapshotDir, snapshotDir, outputFiles);
  checkOutputSource(snapshotDir, outputFiles);
}
Compares build output with snapshot on filesystem.

@param {string} snapshotDir
@param {{ [key: string]: string }} outputFiles