Spys with mirrors!

pkg/unittest/lib/mock.dart

Index: pkg/unittest/lib/mock.dart
===================================================================
--- pkg/unittest/lib/mock.dart	(revision 22345)
+++ pkg/unittest/lib/mock.dart	(working copy)
@@ -102,12 +102,25 @@
  *       }
  *     }
  *
+ * However, there is an even easier way, by calling [Mock.spy], e.g.:
+ *
+ *      var foo = new Foo();
+ *      var spy = new Mock.spy(foo);
+ *      print(spy.bar(1, 2, 3));
+ *
+ * Spys created with Mock.spy do not have user-defined behavior;
+ * they are simply proxies,  and thus will throw an exception if
+ * you call [when]. They capture all calls in the log, so you can
+ * do assertions on their history, such as:
+ *
+ *       spy.getLogs(callsTo('bar')).verify(happenedOnce);
+ *
  * [pub]: http://pub.dartlang.org
  */
 
 library mock;
 
-import 'dart:mirrors' show MirrorSystem;
+import 'dart:mirrors';
 import 'dart:collection' show LinkedHashMap;
 
 import 'matcher.dart';
@@ -1246,6 +1259,9 @@
   /** How to handle unknown method calls - swallow or throw. */
   final bool _throwIfNoBehavior;
 
+  /** For spys, the real object that we are spying on. */
+  Object _realObject;
+
   /** Whether to create an audit log or not. */
   bool _logging;
 
@@ -1286,6 +1302,19 @@
   }
 
   /**
+   * This constructor creates a spy with no user-defined behavior.
+   * This is simply a proxy for a real object that passes calls
+   * through to that real object but captures an audit trail of
+   * calls made to the object that can be queried and validated
+   * later.
+   */
+  Mock.spy(this._realObject, {this.name, this.log})
+    : _behaviors = null,
+     _throwIfNoBehavior = true {
+    logging = true;
+  }
+
+  /**
    * [when] is used to create a new or extend an existing [Behavior].
    * A [CallMatcher] [filter] must be supplied, and the [Behavior]s for
    * that signature are returned (being created first if needed).
@@ -1324,6 +1353,17 @@
         method = method.substring(0, method.length - 1);
       }
     }
+    if (_behaviors == null) { // Spy.
+      var mirror = reflect(_realObject);
+      try {
+        var result = mirror.delegate(invocation);
+        log.add(new LogEntry(name, method, args, Action.PROXY, result));
+        return result;
+      } catch (e) {
+        log.add(new LogEntry(name, method, args, Action.THROW, e));
+        throw e;
+      }
+    }
     bool matchedMethodName = false;
     MatchState matchState = new MatchState();
     for (String k in _behaviors.keys) {
@@ -1360,7 +1400,8 @@
           throw value;
         } else if (action == Action.PROXY) {
           // TODO(gram): Replace all this with:
-          //     var rtn = invocation.invokeOn(value);
+          //     var rtn = reflect(value).apply(invocation.positionalArguments,
+          //         invocation.namedArguments);
           // once that is supported.
           var rtn;
           switch (args.length) {