fix(watch group): Fixed WatchGroup.toString(), added a test.

Author: jbdeboer

lib/change_detection/watch_group.dart

@@ -353,7 +353,7 @@ class WatchGroup implements _EvalWatchList, _WatchGroupList {
     lines.add('WatchGroup[$id](watches: ${watches.join(', ')})');
     var childGroup = _watchGroupHead;
     while (childGroup != null) {
-      lines.add('  ' + childGroup.toString().replace('\n', '\n  '));
+      lines.add('  ' + childGroup.toString().replaceAll('\n', '\n  '));
       childGroup = childGroup._nextWatchGroup;
     }
     return lines.join('\n');

test/change_detection/watch_group_spec.dart

@@ -71,6 +71,16 @@ void main() {
       logger = _logger;
     }));
 
+    it('should have a toString for debugging', () {
+      watchGrp.watch(parse('a'), (v, p) {});
+      watchGrp.newGroup({});
+      expect("$watchGrp").toEqual(
+          'WATCHES: MARKER[null], MARKER[null]\n'
+          'WatchGroup[](watches: MARKER[null])\n'
+          '  WatchGroup[.0](watches: MARKER[null])'
+      );
+    });
+
     describe('watch lifecycle', () {
       it('should prevent reaction fn on removed', () {
         context['a'] = 'hello';