init build flavor capability

example/test_driver/app_test.dart

@@ -20,6 +20,7 @@ Future<void> main() {
     ..customStepParameterDefinitions = [ColourParameter()]
     ..restartAppBetweenScenarios = true
     ..targetAppPath = "test_driver/app.dart"
+    // ..buildFlavor = "staging" // uncomment when using build flavor
     // ..tagExpression = "@smoke" // uncomment to see an example of running scenarios based on tag expressions
     ..exitAfterTestRun = true; // set to false if debugging to exit cleanly
   return GherkinRunner().execute(config);

lib/src/flutter/flutter_run_process_handler.dart

@@ -19,6 +19,7 @@ class FlutterRunProcessHandler extends ProcessHandler {
   List<StreamSubscription> _openSubscriptions = <StreamSubscription>[];
   String _appTarget;
   String _workingDirectory;
+  String _buildFlavor;
 
   void setApplicationTargetFile(String targetPath) {
     _appTarget = targetPath;
@@ -28,10 +29,16 @@ class FlutterRunProcessHandler extends ProcessHandler {
     _workingDirectory = workingDirectory;
   }
 
+  void setBuildFlavor(String buildFlavor) {
+    _buildFlavor = buildFlavor;
+  }
+
   @override
   Future<void> run() async {
+    final buildFlavorArg =
+        _buildFlavor.isNotEmpty ? "--flavor=$_buildFlavor" : "";
     _runningProcess = await Process.start(
-        "flutter", ["run", "--target=$_appTarget"],
+        "flutter", ["run", "--target=$_appTarget", buildFlavorArg],
         workingDirectory: _workingDirectory, runInShell: true);
     _processStdoutStream =
         _runningProcess.stdout.transform(utf8.decoder).asBroadcastStream();

lib/src/flutter/flutter_test_configuration.dart

@@ -22,6 +22,10 @@ class FlutterTestConfiguration extends TestConfiguration {
   /// Defaults to "lib/test_driver/app.dart"
   String targetAppPath = "lib/test_driver/app.dart";
 
+  /// The build flavor to run the tests against
+  /// Defaults to empty
+  String buildFlavor = "";
+
   void setObservatoryDebuggerUri(String uri) => _observatoryDebuggerUri = uri;
 
   Future<FlutterDriver> createFlutterDriver([String dartVmServiceUrl]) async {

lib/src/flutter/hooks/app_runner_hook.dart

@@ -44,6 +44,7 @@ class FlutterAppRunnerHook extends Hook {
   Future<void> _runApp(FlutterTestConfiguration config) async {
     _flutterAppProcess = FlutterRunProcessHandler();
     _flutterAppProcess.setApplicationTargetFile(config.targetAppPath);
+    _flutterAppProcess.setBuildFlavor(config.buildFlavor);
     stdout.writeln(
         "Starting Flutter app under test '${config.targetAppPath}', this might take a few moments");
     await _flutterAppProcess.run();