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/core/build/jest.js

@@ -0,0 +1,41 @@
+'use strict';
+
+Object.defineProperty(exports, '__esModule', {
+  value: true
+});
+Object.defineProperty(exports, 'SearchSource', {
+  enumerable: true,
+  get: function get() {
+    return _SearchSource.default;
+  }
+});
+Object.defineProperty(exports, 'TestScheduler', {
+  enumerable: true,
+  get: function get() {
+    return _TestScheduler.default;
+  }
+});
+Object.defineProperty(exports, 'TestWatcher', {
+  enumerable: true,
+  get: function get() {
+    return _TestWatcher.default;
+  }
+});
+Object.defineProperty(exports, 'runCLI', {
+  enumerable: true,
+  get: function get() {
+    return _cli.runCLI;
+  }
+});
+
+var _SearchSource = _interopRequireDefault(require('./SearchSource'));
+
+var _TestScheduler = _interopRequireDefault(require('./TestScheduler'));
+
+var _TestWatcher = _interopRequireDefault(require('./TestWatcher'));
+
+var _cli = require('./cli');
+
+function _interopRequireDefault(obj) {
+  return obj && obj.__esModule ? obj : {default: obj};
+}