Modify according to dnfield@

Author: CareF

packages/e2e/lib/e2e_driver.dart

@@ -3,6 +3,7 @@ import 'dart:io';
 
 import 'package:e2e/common.dart' as e2e;
 import 'package:flutter_driver/flutter_driver.dart';
+import 'package:meta/meta.dart';
 
 Future<void> main() async => e2eDriver();
 
@@ -19,12 +20,20 @@ Future<void> main() async => e2eDriver();
 /// Future<void> main() async => e2e.e2eDriver();
 ///
 /// ```
+///
+/// `timeout` controls the longest time waited before the test ends, not
+/// necessarily the execution time for the test app.
+///
+/// `traceTimeline` flag controls if timeline and timeline summary should be
+/// collected.
+///
+/// `testName` is used as the file name for the output timeline files.
 Future<void> e2eDriver({
   Duration timeout = const Duration(minutes: 1),
-  String testName,
   bool traceTimeline = false,
+  String testName,
 }) async {
-  print(testName);
+  assert(!traceTimeline || testName != null);
   final FlutterDriver driver = await FlutterDriver.connect();
   String jsonResult;
   Timeline timeline;