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/testPathPatternToRegExp.d.ts

@@ -0,0 +1,9 @@
+/**
+ * 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.
+ */
+declare const _default: (testPathPattern: string) => RegExp;
+export default _default;
+//# sourceMappingURL=testPathPatternToRegExp.d.ts.map