add test related to #264 and #228

lib/src/dart_sdk.dart

Index: lib/src/dart_sdk.dart
diff --git a/lib/src/dart_sdk.dart b/lib/src/dart_sdk.dart
index 6818f952ae46da60cc4afc3c4cf12e156bf9dc50..94099e71b4bbb83166a85e63a7e0ffe7a101a6cd 100644
--- a/lib/src/dart_sdk.dart
+++ b/lib/src/dart_sdk.dart
@@ -156,6 +156,8 @@ final Map<String, String> mockSdkSources = {
         ''',
   'dart:async': '''
         class Future<T> {
+          Future(computation()) {}
+          Future.value(T t) {}
           Future then(callback) {}
         }
         class Stream<T> {}
@@ -164,4 +166,10 @@ final Map<String, String> mockSdkSources = {
         library dart.html;
         class HtmlElement {}
         ''',
+  'dart:math': '''
+        library dart.math;
+        class Random {
+          bool nextBool() {}
+        }
+        ''',
 };