.../Functional/EntityResource/EntityResourceTestBase.php | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/core/modules/rest/tests/src/Functional/EntityResource/EntityResourceTestBase.php b/core/modules/rest/tests/src/Functional/EntityResource/EntityResourceTestBase.php
index 232986b..0e915ce 100644
--- a/core/modules/rest/tests/src/Functional/EntityResource/EntityResourceTestBase.php
+++ b/core/modules/rest/tests/src/Functional/EntityResource/EntityResourceTestBase.php
@@ -86,11 +86,21 @@ public function testGet() {
     $this->provisionEntityResource();
 
     /** @var \Psr\Http\Message\ResponseInterface $response */
-    $url = $this->entity->toUrl();
+    $has_canonical_url = $this->entity->hasLinkTemplate('canonical');
+    $url = $has_canonical_url ? $this->entity->toUrl() : Url::fromUri('base:entity/' . static::$entityType . '/' . $this->entity->id());
 
     // Requesting without the appropriate ?_format query argument.
-    $response = $this->httpClient->get($url->toString());
-    $this->assertSame(200, $response->getStatusCode());
+    try {
+      $response = $this->httpClient->get($url->toString());
+    } catch (ClientException $e) {
+      if (!$has_canonical_url) {
+        $response = $e->getResponse();
+        $this->assertSame(406, $response->getStatusCode());
+      }
+    }
+    if ($has_canonical_url) {
+      $this->assertSame(200, $response->getStatusCode());
+    }
     $this->assertSame(['text/html; charset=UTF-8'], $response->getHeader('Content-Type'));
 
     $url->setOption('query', ['_format' => static::$format]);