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-jasmine2/build/jasmine/SpyStrategy.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.
+ *
+ */
+export default class SpyStrategy {
+    identity: () => string;
+    exec: (...args: Array<any>) => unknown;
+    callThrough: () => unknown;
+    returnValue: (value: unknown) => unknown;
+    returnValues: () => unknown;
+    throwError: (something: string | Error) => unknown;
+    callFake: (fn: Function) => unknown;
+    stub: (fn: Function) => unknown;
+    constructor({ name, fn, getSpy, }?: {
+        name?: string;
+        fn?: Function;
+        getSpy?: () => unknown;
+    });
+}
+//# sourceMappingURL=SpyStrategy.d.ts.map