Add a --pause-after-load flag for debugging.

lib/src/backend/live_test_controller.dart

Index: lib/src/backend/live_test_controller.dart
diff --git a/lib/src/backend/live_test_controller.dart b/lib/src/backend/live_test_controller.dart
index 7eef5f8acfdc71609f9d3266424ebdef280e233b..f562c8e68f86416ebee73cecaad1757fca60f5d9 100644
--- a/lib/src/backend/live_test_controller.dart
+++ b/lib/src/backend/live_test_controller.dart
@@ -151,7 +151,15 @@ class LiveTestController {
   }
 
   /// Emits a line printed by the test over [LiveTest.onPrint].
-  void print(String line) => _onPrintController.add(line);
+  void print(String line) {
+    if (_onPrintController.hasListener) {

[kevmoo, 2015/07/23 20:47:03]

what's a case where the controller has no listener?

[nweiz, 2015/07/23 21:23:00]

After the test package has received a signal, it will unsubscribe everything,
but we may still want to see prints for debugging purposes.

+      _onPrintController.add(line);
+    } else {
+      // Make sure all prints get surfaced one way or another to aid in
+      // debugging.
+      Zone.ROOT.print(line);
+    }
+  }
 
   /// A wrapper for [_onRun] that ensures that it follows the guarantees for
   /// [LiveTest.run].