Check for non-null assignment when checking casts

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

 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 // These tests are for an experimental feature that treats Dart primitive types
 // (int, bool, double, etc.) as non-nullable. This file is not evidence for an
 // intention to officially support non-nullable primitives in Dart (or general
 // NNBD, for that matter) so don't get too crazy about it.
 
 library analyzer.test.src.task.non_null_primitives.checker_test;
@@ skipping 88 matching lines @@
 
 main() {
   var languages = new MyList();
   for (int i = 0; i < languages.length; ++i) {
     print(languages[i]);
   }
 }
 ''');
   }
 
+  void test_compoundAssignment() {
+    addFile('''
+void main() {
+  int i = 1;
+  i += 2;
+  /*error:STATIC_TYPE_ERROR*/i += null;
+  print(i);
+}
+''');
+    check(nonnullableTypes: <String>['dart:core,int']);
+  }
+
+  void test_forEach() {
+    addFile('''
+void main() {
+  var ints = <num>[1, 2, 3, null];
+  for (int /*error:INVALID_ASSIGNMENT*/i in ints) {
+    print(i);
+  }
+}
+''');
+    check(nonnullableTypes: <String>['dart:core,int']);
+  }
+
   void test_initialize_nonnullable_with_null() {
     addFile('int x = /*error:INVALID_ASSIGNMENT*/null;');
     check(nonnullableTypes: <String>['dart:core,int']);
   }
 
   void test_initialize_nonnullable_with_valid_value() {
     addFile('int x = 0;');
     check(nonnullableTypes: <String>['dart:core,int']);
   }
 
@@ skipping 163 matching lines @@
   legs.insert("goat", 4);
   legs.insert("chicken", 2);
 
   int x = legs.get("goat"); // This should not produce an error.
   int y = legs.get("sheep"); // TODO(stanm): Runtime error here.
 }
 ''');
     check(nonnullableTypes: <String>['dart:core,int']);
   }
 }