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/core/build/testSchedulerHelper.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.
+ */
+import { Config } from '@jest/types';
+import { Test } from 'jest-runner';
+export declare function shouldRunInBand(tests: Array<Test>, timings: Array<number>, { detectOpenHandles, maxWorkers, watch, watchAll }: Config.GlobalConfig): boolean;
+//# sourceMappingURL=testSchedulerHelper.d.ts.map