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-watcher/build/BaseWatchPlugin.d.ts

@@ -0,0 +1,23 @@
+/**
+ * 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.
+ */
+/// <reference types="node" />
+import { Config } from '@jest/types';
+import { JestHookSubscriber, UpdateConfigCallback, UsageData, WatchPlugin } from './types';
+declare class BaseWatchPlugin implements WatchPlugin {
+    protected _stdin: NodeJS.ReadStream;
+    protected _stdout: NodeJS.WriteStream;
+    constructor({ stdin, stdout, }: {
+        stdin: NodeJS.ReadStream;
+        stdout: NodeJS.WriteStream;
+    });
+    apply(_hooks: JestHookSubscriber): void;
+    getUsageInfo(_globalConfig: Config.GlobalConfig): UsageData | null;
+    onKey(_key: string): void;
+    run(_globalConfig: Config.GlobalConfig, _updateConfigAndRun: UpdateConfigCallback): Promise<void | boolean>;
+}
+export default BaseWatchPlugin;
+//# sourceMappingURL=BaseWatchPlugin.d.ts.map