pkg/unittest: fixed asserts around currentTestCase

pkg/unittest/lib/src/config.dart

Index: pkg/unittest/lib/src/config.dart
diff --git a/pkg/unittest/lib/src/config.dart b/pkg/unittest/lib/src/config.dart
index cbedfb3d7cba3430b87fbd63de62794b089c60e0..01b97a381492582bbd06f6013d8104b79d968427 100644
--- a/pkg/unittest/lib/src/config.dart
+++ b/pkg/unittest/lib/src/config.dart
@@ -52,6 +52,8 @@ class Configuration {
    * a test suite.
    */
   void onTestStart(TestCase testCase) {
+    assert(testCase != null);
+    assert(_currentTestCase == null);
     _currentTestCase = testCase;
   }
 
@@ -60,6 +62,8 @@ class Configuration {
    * a test suite.
    */
   void onTestResult(TestCase testCase) {
+    assert(testCase != null);
+    assert(_currentTestCase == null || _currentTestCase == testCase);

[gram, 2013/02/26 21:42:13]

This is just begging for an XOR logical operator, isn't it!

     _currentTestCase = null;
   }