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-config/build/validatePattern.js

@@ -0,0 +1,25 @@
+'use strict';
+
+Object.defineProperty(exports, '__esModule', {
+  value: true
+});
+exports.default = validatePattern;
+
+/**
+ * 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 validatePattern(pattern) {
+  if (pattern) {
+    try {
+      // eslint-disable-next-line no-new
+      new RegExp(pattern, 'i');
+    } catch (e) {
+      return false;
+    }
+  }
+
+  return true;
+}