Disallow assigning null to non-nullable variables

pkg/analyzer/test/src/task/strong/non_null_checker_test.dart

Index: pkg/analyzer/test/src/task/strong/non_null_checker_test.dart
diff --git a/pkg/analyzer/test/src/task/strong/non_null_checker_test.dart b/pkg/analyzer/test/src/task/strong/non_null_checker_test.dart
index 7b9b933973941f16ec1a328330c89e10378b925a..9e222ce95bdadbb9e52b4efde8079fc8e39f3f72 100644
--- a/pkg/analyzer/test/src/task/strong/non_null_checker_test.dart
+++ b/pkg/analyzer/test/src/task/strong/non_null_checker_test.dart
@@ -48,10 +48,19 @@ main() {
     checkFile('''int x = null;''');
   }
 
-  @failingTest
   void test_nonnullableTypes() {
     // If `int`s are non-nullable, then this code should throw an error.
+    addFile('''int x;''');

[Jennifer Messerly, 2016/08/03 18:06:56]

if it's a 1-liner, you can use single quotes. The triple quotes are intended to
help with newlines

[stanm, 2016/08/03 18:46:20]

I was too lazy to think and just copied code over :)

     addFile('''int x = /*error:INVALID_ASSIGNMENT*/null;''');
+    addFile('''int x = 0;''');
+    addFile('''
+int x = 0;
+
+main() {
+  x = 1;
+  x = /*error:INVALID_ASSIGNMENT*/null;
+}
+''');
     check(nonnullableTypes: <String>['dart:core,int']);
   }
 }