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-validate/build/validate.d.ts

@@ -0,0 +1,15 @@
+/**
+ * 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.
+ */
+import { ValidationOptions } from './types';
+declare const validate: (config: {
+    [key: string]: any;
+}, options: ValidationOptions) => {
+    hasDeprecationWarnings: boolean;
+    isValid: boolean;
+};
+export default validate;
+//# sourceMappingURL=validate.d.ts.map