code: function copyAssetToContext(src, dest, context) {
      var sourceAsset = path.join(testDir, src);
      var targetAsset = path.join(context.dir, dest);
  
      if (!fs.existsSync(sourceAsset)) {
          // The source asset requested is missing
          throw new Error("The test asset is missing");
      }
  
      // Attempt to copy the asset
      fs.copySync(sourceAsset, targetAsset);
  
      if (!fs.existsSync(targetAsset)) {
          // The target asset was not copied successfully
          throw new Error("The test asset could not be copied");
      }
  }
docs: Look for a test asset, and if it exists, copy it to the
  test context at the given location.