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/test-result/build/helpers.d.ts

@@ -0,0 +1,11 @@
+/**
+ * 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 { AggregatedResult, SerializableError, TestResult } from './types';
+export declare const makeEmptyAggregatedTestResult: () => AggregatedResult;
+export declare const buildFailureTestResult: (testPath: string, err: SerializableError) => TestResult;
+export declare const addResult: (aggregatedResults: AggregatedResult, testResult: TestResult) => void;
+//# sourceMappingURL=helpers.d.ts.map