add comments of message array, add utest.

@@ -50,7 +50,13 @@ public:
     SrsSharedPtrMessage** msgs;
     int size;
 public:
+    /**
+    * create msg array, initialize array to NULL ptrs.
+    */
     SrsSharedPtrMessageArray(int _size);
+    /**
+    * free the msgs not sent out(not NULL).
+    */
     virtual ~SrsSharedPtrMessageArray();
 };
 

@@ -413,5 +413,16 @@ VOID TEST(ProtocolMsgArrayTest, MessageArray)
         EXPECT_EQ(3, msg.count());
     }
     EXPECT_EQ(0, msg.count());
+    
+    if (true) {
+        SrsSharedPtrMessageArray arr(3);
+        
+        arr.msgs[0] = msg.copy();
+        EXPECT_EQ(1, msg.count());
+        
+        arr.msgs[2] = msg.copy();
+        EXPECT_EQ(2, msg.count());
+    }
+    EXPECT_EQ(0, msg.count());
 }