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/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.
+ */
+import { Config } from '@jest/types';
+import { OnTestFailure, OnTestStart, OnTestSuccess, Test as JestTest, TestRunnerContext, TestRunnerOptions, TestWatcher } from './types';
+declare namespace TestRunner {
+    type Test = JestTest;
+}
+declare class TestRunner {
+    private _globalConfig;
+    private _context;
+    constructor(globalConfig: Config.GlobalConfig, context?: TestRunnerContext);
+    runTests(tests: Array<JestTest>, watcher: TestWatcher, onStart: OnTestStart, onResult: OnTestSuccess, onFailure: OnTestFailure, options: TestRunnerOptions): Promise<void>;
+    private _createInBandTestRun;
+    private _createParallelTestRun;
+}
+export = TestRunner;
+//# sourceMappingURL=index.d.ts.map