diff --git a/core/modules/rest/tests/src/Unit/EventSubscriber/ResourceResponseSubscriberTest.php b/core/modules/rest/tests/src/Unit/EventSubscriber/ResourceResponseSubscriberTest.php
index d09fdced4c..ea93d78988 100644
--- a/core/modules/rest/tests/src/Unit/EventSubscriber/ResourceResponseSubscriberTest.php
+++ b/core/modules/rest/tests/src/Unit/EventSubscriber/ResourceResponseSubscriberTest.php
@@ -92,8 +92,19 @@ public function testResponseFormat($methods, array $supported_formats, $request_
       if ($request_format) {
         $request->setRequestFormat($request_format);
       }
-      $route_requirement_key_format = $request->isMethodCacheable() ? '_format' : '_content_type_format';
-      $route_match = new RouteMatch('test', new Route('/rest/test', ['_rest_resource_config' => $this->randomMachineName()], [$route_requirement_key_format => implode('|', $supported_formats)]));
+
+      // Add the supported formats as allowed response formats so requests can
+      // receive responses in a different format.
+      $supported_format_string = implode('|', $supported_formats);
+      $route_requirements = [
+        '_format' => $supported_format_string,
+      ];
+
+      if (!$request->isMethodCacheable()) {
+        $route_requirements['_content_type_format'] = $supported_format_string;
+      }
+
+      $route_match = new RouteMatch('test', new Route('/rest/test', ['_rest_resource_config' => $this->randomMachineName()], $route_requirements));
 
       $resource_response_subscriber = new ResourceResponseSubscriber(
         $this->prophesize(SerializerInterface::class)->reveal(),
@@ -129,8 +140,19 @@ public function testOnResponseWithCacheableResponse($methods, array $supported_f
       if ($request_format) {
         $request->setRequestFormat($request_format);
       }
-      $route_requirement_key_format = $request->isMethodCacheable() ? '_format' : '_content_type_format';
-      $route_match = new RouteMatch('test', new Route('/rest/test', ['_rest_resource_config' => $rest_config_name], [$route_requirement_key_format => implode('|', $supported_formats)]));
+
+      // Add the supported formats as allowed response formats so requests can
+      // receive responses in a different format.
+      $supported_format_string = implode('|', $supported_formats);
+      $route_requirements = [
+        '_format' => $supported_format_string,
+      ];
+
+      if (!$request->isMethodCacheable()) {
+        $route_requirements['_content_type_format'] = $supported_format_string;
+      }
+
+      $route_match = new RouteMatch('test', new Route('/rest/test', ['_rest_resource_config' => $this->randomMachineName()], $route_requirements));
 
       // The RequestHandler must return a ResourceResponseInterface object.
       $handler_response = new ResourceResponse($method !== 'DELETE' ? ['REST' => 'Drupal'] : NULL);
@@ -179,8 +201,19 @@ public function testOnResponseWithUncacheableResponse($methods, array $supported
       if ($request_format) {
         $request->setRequestFormat($request_format);
       }
-      $route_requirement_key_format = $request->isMethodCacheable() ? '_format' : '_content_type_format';
-      $route_match = new RouteMatch('test', new Route('/rest/test', ['_rest_resource_config' => $rest_config_name], [$route_requirement_key_format => implode('|', $supported_formats)]));
+
+      // Add the supported formats as allowed response formats so requests can
+      // receive responses in a different format.
+      $supported_format_string = implode('|', $supported_formats);
+      $route_requirements = [
+        '_format' => $supported_format_string,
+      ];
+
+      if (!$request->isMethodCacheable()) {
+        $route_requirements['_content_type_format'] = $supported_format_string;
+      }
+
+      $route_match = new RouteMatch('test', new Route('/rest/test', ['_rest_resource_config' => $this->randomMachineName()], $route_requirements));
 
       // The RequestHandler must return a ResourceResponseInterface object.
       $handler_response = new ModifiedResourceResponse($method !== 'DELETE' ? ['REST' => 'Drupal'] : NULL);