Do not complete future if already completed; better handle null messages

lib/src/dart_dev_cli.dart

@@ -182,9 +182,9 @@ Future _run(List<String> args) async {
 
   reporter.log('');
   if (result.successful) {
-    reporter.success(result.message ?? '', shout: true);
+    reporter.success(result.message, shout: true);
   } else {
-    reporter.error(result.message ?? 'The task did not succeed.', shout: true);
+    reporter.error(result.message, shout: true);
     exitCode = 1;
   }
 }

lib/src/reporter.dart

@@ -87,19 +87,26 @@ class Reporter {
   }
 
   void error(String message, {bool shout: false}) {
+    message = message ?? 'An error was encountered running the task.';
     _log(stderr, colorRed(message), shout: shout);
   }
 
   void success(String message, {bool shout: false}) {
+    if (message == null) {
+      return;
+    }
     log(colorGreen(message), shout: shout);
   }
 
   void warning(String message, {bool shout: false}) {
+    if (message == null) {
+      return;
+    }
     _log(stderr, colorYellow(message), shout: shout);
   }
 
   String _colorMessage(AnsiPen pen, String message) =>
-      color && message.isNotEmpty ? pen(message) : message;
+      color && message != null && message.isNotEmpty ? pen(message) : message;
 
   void _log(IOSink sink, String message, {bool shout: false}) {
     if (quiet && !shout) return;

lib/src/tasks/test/api.dart

@@ -106,10 +106,12 @@ TestTask test({
       task.successful = code <= 0;
 
       if (!task.successful) {
-        task.testSummary = 'An error was encountered when running tests.';
+//        task.testSummary = 'An error was encountered when running tests.';
       }
 
-      outputProcessed.complete();
+      if (!outputProcessed.isCompleted) {
+        outputProcessed.complete();
+      }
     }
   });