Implemented message sink block for unit testing
diff --git a/grc/misc_utils/gsm_message_sink.xml b/grc/misc_utils/gsm_message_sink.xml
new file mode 100644
index 0000000..e0d6ac0
--- /dev/null
+++ b/grc/misc_utils/gsm_message_sink.xml
@@ -0,0 +1,19 @@
+<?xml version="1.0"?>
+<block>
+ <name>Message Sink</name>
+ <key>gsm_message_sink</key>
+ <import>import grgsm</import>
+ <make>grgsm.message_sink()</make>
+
+ <sink>
+ <name>in</name>
+ <type>message</type>
+ </sink>
+
+ <doc>
+This block is a message sink for testing purposes.
+
+The data can be retrieved using function get_messages()
+
+ </doc>
+</block>