Added checks to make sure the specified track exists

Added precondition checks to validate input files and paths to return more informative error messages as per #2

node_modules/jest-util/build/createDirectory.js

@@ -0,0 +1,36 @@
+'use strict';
+
+Object.defineProperty(exports, '__esModule', {
+  value: true
+});
+exports.default = createDirectory;
+
+function _mkdirp() {
+  const data = _interopRequireDefault(require('mkdirp'));
+
+  _mkdirp = function _mkdirp() {
+    return data;
+  };
+
+  return data;
+}
+
+function _interopRequireDefault(obj) {
+  return obj && obj.__esModule ? obj : {default: obj};
+}
+
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+function createDirectory(path) {
+  try {
+    _mkdirp().default.sync(path, '777');
+  } catch (e) {
+    if (e.code !== 'EEXIST') {
+      throw e;
+    }
+  }
+}