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-serializer/build/index.d.ts

@@ -0,0 +1,21 @@
+/**
+ * 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 path="../v8.d.ts" />
+/// <reference types="node" />
+declare type Path = string;
+export declare function deserialize(buffer: Buffer): any;
+export declare function serialize(content: unknown): Buffer;
+export declare function readFileSync(filePath: Path): any;
+export declare function writeFileSync(filePath: Path, content: any): void;
+declare const _default: {
+    deserialize: typeof deserialize;
+    readFileSync: typeof readFileSync;
+    serialize: typeof serialize;
+    writeFileSync: typeof writeFileSync;
+};
+export default _default;
+//# sourceMappingURL=index.d.ts.map