diff --git a/emgauwa-core.conf.d/conf_d_working.conf b/emgauwa-core.conf.d/conf_d_working.conf
new file mode 100644
index 0000000..dc4616a
--- /dev/null
+++ b/emgauwa-core.conf.d/conf_d_working.conf
@@ -0,0 +1,3 @@
+[core]
+not-found-content = "CONF.D WORKING"
+not-found-content-type = "text/plain"
diff --git a/tests/emgauwa-core-testing.conf b/tests/emgauwa-core-testing.conf
index f475720..c3896b2 100644
--- a/tests/emgauwa-core-testing.conf
+++ b/tests/emgauwa-core-testing.conf
@@ -1,10 +1,9 @@
 [core]
 database = "emgauwa-core.sqlite"
+include = "../emgauwa-core-testing.conf.d"
 content-dir = "."
 not-found-file = "404.html"
 not-found-file-mime = "text/html"
-not-found-content = "404 - NOT FOUND"
-not-found-content-type = "text/plain"
 
 [ports]
 server = 5000
diff --git a/tests/emgauwa-core-testing.conf.d/conf_d_working.conf b/tests/emgauwa-core-testing.conf.d/conf_d_working.conf
new file mode 100644
index 0000000..ac1dfee
--- /dev/null
+++ b/tests/emgauwa-core-testing.conf.d/conf_d_working.conf
@@ -0,0 +1,3 @@
+[core]
+not-found-content = '{"msg": "conf.d working"}'
+not-found-content-type = "application/json"
diff --git a/tests/tavern_tests/0.1.test_basics.tavern.yaml b/tests/tavern_tests/0.1.test_basics.tavern.yaml
index 14ac8b5..8eff061 100644
--- a/tests/tavern_tests/0.1.test_basics.tavern.yaml
+++ b/tests/tavern_tests/0.1.test_basics.tavern.yaml
@@ -14,3 +14,12 @@ stages:
     method: GET
   response:
     status_code: 404
+
+- name: "[test_basics] verify conf.d by 404"
+  request:
+    url: "http://localhost:5000/invalid_url_for_testing_do_not_use"
+    method: GET
+  response:
+    status_code: 404
+    json:
+        msg: "conf.d working"