diff --git a/README.rst b/README.rst
index 981a1ea5..1b36772f 100644
--- a/README.rst
+++ b/README.rst
@@ -52,10 +52,11 @@ Contributing quickstart
 Assuming Git, Vagrant_ and VirtualBox_ are installed:
 
 ::
-   host$ git clone git@github.com:snowplow/snowplow-python-tracker.git
-   host$ vagrant up && vagrant ssh
-  guest$ cd /vagrant
-  guest$ ./run-tests.sh
+
+    host$ git clone git@github.com:snowplow/snowplow-python-tracker.git
+    host$ vagrant up && vagrant ssh
+    guest$ cd /vagrant
+    guest$ ./run-tests.sh
 
 .. _Vagrant: http://docs.vagrantup.com/v2/installation/index.html
 .. _VirtualBox: https://www.virtualbox.org/wiki/Downloads
@@ -64,7 +65,8 @@ Publishing
 ##########
 
 ::
-   host$ vagrant push
+
+    host$ vagrant push
 
 Copyright and license
 #####################
diff --git a/requirements-test.txt b/requirements-test.txt
new file mode 100644
index 00000000..e4d3153e
--- /dev/null
+++ b/requirements-test.txt
@@ -0,0 +1,3 @@
+pytest
+httmock
+freezegun
diff --git a/snowplow_tracker/subject.py b/snowplow_tracker/subject.py
index 64c5374e..34212124 100644
--- a/snowplow_tracker/subject.py
+++ b/snowplow_tracker/subject.py
@@ -162,3 +162,17 @@ def set_network_user_id(self, nuid):
         """
         self.standard_nv_pairs["tnuid"] = nuid
         return self
+
+    @contract
+    def set_txn_id(self, txn_id):
+        """
+            Set Transaction ID set client-side, used to de-dupe records.
+
+            :param txn_id:          Network user ID
+            :type  txn_id:          int
+            :rtype:                 subject
+        """
+        # Unfortunatly real name of this field is `tid`. This difference in
+        # documentation is little confusing.
+        self.standard_nv_pairs["tid"] = txn_id
+        return self
diff --git a/snowplow_tracker/test/integration/test_integration.py b/snowplow_tracker/test/integration/test_integration.py
index f5095aa7..103ad1cc 100644
--- a/snowplow_tracker/test/integration/test_integration.py
+++ b/snowplow_tracker/test/integration/test_integration.py
@@ -80,7 +80,7 @@ def test_integration_page_view(self):
             t.track_page_view("http://savethearctic.org", "Save The Arctic", "http://referrer.com")
         expected_fields = {"e": "pv", "page": "Save+The+Arctic", "url": "http%3A%2F%2Fsavethearctic.org", "refr": "http%3A%2F%2Freferrer.com"}
         for key in expected_fields:
-            self.assertEquals(from_querystring(key, querystrings[-1]), expected_fields[key])            
+            self.assertEquals(from_querystring(key, querystrings[-1]), expected_fields[key])
 
     def test_integration_ecommerce_transaction_item(self):
         t = tracker.Tracker([default_emitter], default_subject)
@@ -94,7 +94,7 @@ def test_integration_ecommerce_transaction(self):
         t = tracker.Tracker([default_emitter], default_subject)
         with HTTMock(pass_response_content):
             t.track_ecommerce_transaction("6a8078be", 35, city="London", currency="GBP", items=
-                [{  
+                [{
                     "sku": "pbz0026",
                     "price": 20,
                     "quantity": 1
@@ -102,7 +102,7 @@ def test_integration_ecommerce_transaction(self):
                 {
                     "sku": "pbz0038",
                     "price": 15,
-                    "quantity": 1  
+                    "quantity": 1
                 }])
 
         expected_fields = {"e": "tr", "tr_id": "6a8078be", "tr_tt": "35", "tr_ci": "London", "tr_cu": "GBP"}
@@ -124,7 +124,7 @@ def test_integration_screen_view(self):
         with HTTMock(pass_response_content):
             t.track_screen_view("Game HUD 2", id_="534")
         expected_fields = {"e": "ue"}
-        for key in expected_fields:          
+        for key in expected_fields:
             self.assertEquals(from_querystring(key, querystrings[-1]), expected_fields[key])
         envelope_string = from_querystring("ue_pr", querystrings[-1])
         envelope = json.loads(unquote_plus(envelope_string))
@@ -184,7 +184,7 @@ def test_integration_context_non_base64(self):
             "schema": "iglu:com.snowplowanalytics.snowplow/contexts/jsonschema/1-0-1",
             "data":[{"schema": "iglu:com.example/user/jsonschema/2-0-3", "data": {"user_type": "tester"}}]
         })
-    
+
     def test_integration_context_base64(self):
         t = tracker.Tracker([default_emitter], default_subject, encode_base64=True)
         with HTTMock(pass_response_content):
@@ -195,7 +195,7 @@ def test_integration_context_base64(self):
             "schema": "iglu:com.snowplowanalytics.snowplow/contexts/jsonschema/1-0-1",
             "data":[{"schema": "iglu:com.example/user/jsonschema/2-0-3", "data": {"user_type": "tester"}}]
         })
-    
+
     def test_integration_standard_nv_pairs(self):
         s = subject.Subject()
         s.set_platform("mob")
@@ -235,6 +235,22 @@ def test_integration_identification_methods(self):
         for key in expected_fields:
             self.assertEquals(from_querystring(key, querystrings[-1]), expected_fields[key])
 
+    def test_integration_transaction(self):
+        s = subject.Subject()
+        s.set_domain_user_id("4616bfb38f872d16")
+        s.set_txn_id(10000)
+
+        t = tracker.Tracker([emitters.Emitter("localhost")], s, "cf", app_id="angry-birds-android")
+        with HTTMock(pass_response_content):
+            t.track_page_view("localhost", "local host")
+        expected_fields = {
+            "duid": "4616bfb38f872d16",
+            "tid": '10000'
+        }
+        for key in expected_fields:
+            self.assertEquals(from_querystring(key, querystrings[-1]), expected_fields[key])
+
+
     def test_integration_redis_default(self):
         r = redis.StrictRedis()
         t = tracker.Tracker([emitters.RedisEmitter()], default_subject)