diff --git a/tests/smoke.php b/tests/smoke.php
index b25a339..05d18bb 100644
--- a/tests/smoke.php
+++ b/tests/smoke.php
@@ -211,6 +211,18 @@ $ours   = array_filter(
 );
 wc_edm_ok( 'the REST routes are registered', count( $ours ) > 0, 'namespace ' . WC_EDM_REST_API::REST_NAMESPACE );
 
+// The namespace spelled out, NOT compared to the constant it came from. The
+// filter above derives what it looks for from REST_NAMESPACE, so it agrees
+// with itself whatever that constant says: rename it and the routes are still
+// "registered", while every caller that already integrated against
+// wc-edm/v1 gets a 404 and nothing here goes red. This is the one string in
+// the plugin that somebody else's code depends on by name.
+wc_edm_is(
+	'and under the namespace callers already integrated against',
+	'wc-edm/v1',
+	WC_EDM_REST_API::REST_NAMESPACE
+);
+
 $request  = new WP_REST_Request( 'GET', '/' . WC_EDM_REST_API::REST_NAMESPACE . '/groups' );
 $response = rest_get_server()->dispatch( $request );
 wc_edm_is( 'and they refuse an unauthenticated caller', 401, $response->get_status() );