[flutter_tools] retry the driver launch of the application up to 3 times. (flutter#68334)

We'd like to see how many of these flakes are transient and how many involve the device/machine getting temporarily wedged. Add a retry with no delay to see if it is possible to add sufficient error handling to startApp/installApp to handle this.

Author: Jonah Williams

packages/flutter_tools/lib/src/commands/drive.dart

@@ -246,7 +246,19 @@ class DriveCommand extends RunCommandBase {
         webUri = residentRunner.uri;
       }
 
-      final LaunchResult result = await appStarter(this, webUri, package, applicationBinary != null);
+      // Attempt to launch the application up to 3 times, to validate whether it
+      // is possible to reduce flakiness by hardnening the launch code.
+      int attempt = 0;
+      LaunchResult result;
+      while (attempt < 3) {
+        // On attempts past 1, assume the application is built correctly and re-use it.
+        result = await appStarter(this, webUri, package, applicationBinary != null || attempt > 0);
+        if (result != null) {
+          break;
+        }
+        attempt += 1;
+        globals.printError('Application failed to start on attempt: $attempt');
+      }
       if (result == null) {
         throwToolExit('Application failed to start. Will not run test. Quitting.', exitCode: 1);
       }

packages/flutter_tools/test/commands.shard/hermetic/drive_test.dart

@@ -99,7 +99,7 @@ void main() {
 
     testUsingContext('returns 1 when app fails to run', () async {
       testDeviceManager.addDevice(MockDevice());
-      appStarter = expectAsync4((DriveCommand command, Uri webUri, ApplicationPackage package, bool prebuiltApplication) async => null);
+      appStarter = expectAsync4((DriveCommand command, Uri webUri, ApplicationPackage package, bool prebuiltApplication) async => null, count: 3);
 
       final String testApp = globals.fs.path.join(tempDir.path, 'test_driver', 'e2e.dart');
       final String testFile = globals.fs.path.join(tempDir.path, 'test_driver', 'e2e_test.dart');