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-runner/build/runTest.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.
+ *
+ */
+import { Config } from '@jest/types';
+import { TestResult } from '@jest/test-result';
+import Resolver from 'jest-resolve';
+import { TestRunnerContext } from './types';
+export default function runTest(path: Config.Path, globalConfig: Config.GlobalConfig, config: Config.ProjectConfig, resolver: Resolver, context?: TestRunnerContext): Promise<TestResult>;
+//# sourceMappingURL=runTest.d.ts.map