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-each/build/table/template.d.ts

@@ -0,0 +1,13 @@
+/**
+ * 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: (title: string, headings: string[], row: unknown[]) => {
+    title: string;
+    arguments: unknown[];
+}[];
+export default _default;
+//# sourceMappingURL=template.d.ts.map