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/preRunMessage.d.ts

@@ -0,0 +1,10 @@
+/**
+ * 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.
+ */
+/// <reference types="node" />
+export declare const print: (stream: NodeJS.WritableStream) => void;
+export declare const remove: (stream: NodeJS.WritableStream) => void;
+//# sourceMappingURL=preRunMessage.d.ts.map