Fix initialization order in Django app

ddtrace/contrib/django/apps.py

@@ -31,13 +31,6 @@ def ready(self):
         if settings.TAGS:
             tracer.set_tags(settings.TAGS)
 
-        # define the service details
-        tracer.set_service_info(
-            app='django',
-            app_type=AppTypes.web,
-            service=settings.DEFAULT_SERVICE,
-        )
-
         # configure the tracer instance
         # TODO[manu]: we may use configure() but because it creates a new
         # AgentWriter, it breaks all tests. The configure() behavior must
@@ -46,6 +39,13 @@ def ready(self):
         tracer.writer.api.hostname = settings.AGENT_HOSTNAME
         tracer.writer.api.port = settings.AGENT_PORT
 
+        # define the service details
+        tracer.set_service_info(
+            app='django',
+            app_type=AppTypes.web,
+            service=settings.DEFAULT_SERVICE,
+        )
+
         if settings.AUTO_INSTRUMENT:
             # trace Django internals
             insert_exception_middleware()

tests/contrib/django/test_tracing_disabled.py

@@ -0,0 +1,40 @@
+# 3rd party
+from django.apps import apps
+from django.test import TestCase, override_settings
+
+# project
+from ddtrace.tracer import Tracer
+from ddtrace.contrib.django.conf import settings
+
+# testing
+from ...test_tracer import DummyWriter
+
+
+class DjangoTracingDisabledTest(TestCase):
+    def setUp(self):
+        tracer = Tracer()
+        tracer.writer = DummyWriter()
+        self.tracer = tracer
+        # Backup the old conf
+        self.backupTracer = settings.TRACER
+        self.backupEnabled = settings.ENABLED
+        # Disable tracing
+        settings.ENABLED = False
+        settings.TRACER = tracer
+        # Restart the app
+        app = apps.get_app_config('datadog_django')
+        app.ready()
+
+    def tearDown(self):
+        # Reset the original settings
+        settings.ENABLED = self.backupEnabled
+        settings.TRACER = self.backupTracer
+
+    def test_no_service_info_is_written(self):
+        services = self.tracer.writer.pop_services()
+        assert len(services) == 0
+
+    def test_no_trace_is_written(self):
+        settings.TRACER.trace("client.testing").finish()
+        traces = self.tracer.writer.pop_traces()
+        assert len(traces) == 0