Get all tests running via the test runner.

test/invoker_test.dart

Index: test/invoker_test.dart
diff --git a/test/invoker_test.dart b/test/invoker_test.dart
index 63823b2a3729b4ea3f3c10555bdb974be1d5c67a..b3a655b8df393a24b01d82163a1d2d152d277167 100644
--- a/test/invoker_test.dart
+++ b/test/invoker_test.dart
@@ -20,8 +20,9 @@ void main() {
   });
 
   group("Invoker.current", () {
+    var invoker = Invoker.current;
     test("returns null outside of a test body", () {
-      expect(Invoker.current, isNull);
+      expect(invoker, isNull);
     });
 
     test("returns the current invoker in a test body", () {