Implemented message sink block for unit testing
diff --git a/grc/gsm_block_tree.xml b/grc/gsm_block_tree.xml
index 5837ce2..2864e4d 100644
--- a/grc/gsm_block_tree.xml
+++ b/grc/gsm_block_tree.xml
@@ -52,6 +52,7 @@
       <block>gsm_clock_offset_corrector</block>
       <block>gsm_tmsi_dumper</block>
       <block>gsm_message_source</block>
+      <block>gsm_message_sink</block>
     </cat>
   </cat>
 </cat>
diff --git a/grc/misc_utils/CMakeLists.txt b/grc/misc_utils/CMakeLists.txt
index 403a321..5dd4c1b 100644
--- a/grc/misc_utils/CMakeLists.txt
+++ b/grc/misc_utils/CMakeLists.txt
@@ -29,6 +29,7 @@
     gsm_burst_sink.xml
     gsm_burst_source.xml
     gsm_burst_source_qa.xml
-    gsm_burst_sink_qa.xml 
-    gsm_message_source.xml DESTINATION share/gnuradio/grc/blocks
+    gsm_burst_sink_qa.xml
+    gsm_message_source.xml
+    gsm_message_sink.xml DESTINATION share/gnuradio/grc/blocks
 )
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>