.../modules/rest/tests/src/Functional/CookieResourceTestTrait.php | 2 +-
 .../src/Functional/EntityResource/EntityResourceTestBase.php      | 8 ++++----
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/core/modules/rest/tests/src/Functional/CookieResourceTestTrait.php b/core/modules/rest/tests/src/Functional/CookieResourceTestTrait.php
index c231ffb..18dc296 100644
--- a/core/modules/rest/tests/src/Functional/CookieResourceTestTrait.php
+++ b/core/modules/rest/tests/src/Functional/CookieResourceTestTrait.php
@@ -71,7 +71,7 @@ protected function initAuthentication() {
     $this->sessionCookie = explode(';', $response->getHeader('Set-Cookie')[0], 2)[0];
 
     // Parse and store the CSRF token and logout token.
-    $data = $this->serializer->decode($response->getBody()->getContents(), static::$format);
+    $data = $this->serializer->decode((string)$response->getBody(), static::$format);
     $this->csrfToken = $data['csrf_token'];
     $this->logoutToken = $data['logout_token'];
   }
diff --git a/core/modules/rest/tests/src/Functional/EntityResource/EntityResourceTestBase.php b/core/modules/rest/tests/src/Functional/EntityResource/EntityResourceTestBase.php
index 2d43a66..81cbdf5 100644
--- a/core/modules/rest/tests/src/Functional/EntityResource/EntityResourceTestBase.php
+++ b/core/modules/rest/tests/src/Functional/EntityResource/EntityResourceTestBase.php
@@ -502,7 +502,7 @@ public function testPost() {
     if ($has_canonical_url) {
       $this->assertSame(415, $response->getStatusCode());
       $this->assertSame(['text/html; charset=UTF-8'], $response->getHeader('Content-Type'));
-      $this->assertContains(htmlspecialchars('No "Content-Type" request header specified'), $response->getBody()->getContents());
+      $this->assertContains(htmlspecialchars('No "Content-Type" request header specified'), (string) $response->getBody());
     }
     else {
       $this->assertResourceErrorResponse(415, 'No "Content-Type" request header specified', $response);
@@ -702,7 +702,7 @@ public function testPatch() {
     if ($has_canonical_url) {
       $this->assertSame(415, $response->getStatusCode());
       $this->assertSame(['text/html; charset=UTF-8'], $response->getHeader('Content-Type'));
-      $this->assertTrue(FALSE !== strpos($response->getBody()->getContents(), htmlspecialchars('No "Content-Type" request header specified')));
+      $this->assertTrue(FALSE !== strpos((string) $response->getBody(), htmlspecialchars('No "Content-Type" request header specified')));
     }
     else {
       $this->assertResourceErrorResponse(415, 'No "Content-Type" request header specified', $response);
@@ -928,7 +928,7 @@ public function testDelete() {
     $this->assertSame(204, $response->getStatusCode());
     // @todo Uncomment the following line when https://www.drupal.org/node/2821711 is fixed.
     // $this->assertSame(FALSE, $response->hasHeader('Content-Type'));
-    $this->assertSame('', $response->getBody()->getContents());
+    $this->assertSame('', (string) $response->getBody());
     $this->assertFalse($response->hasHeader('X-Drupal-Cache'));
 
 
@@ -953,7 +953,7 @@ public function testDelete() {
     $this->assertSame(204, $response->getStatusCode());
     // @todo Uncomment the following line when https://www.drupal.org/node/2821711 is fixed.
     // $this->assertSame(FALSE, $response->hasHeader('Content-Type'));
-    $this->assertSame('', $response->getBody()->getContents());
+    $this->assertSame('', (string) $response->getBody());
     $this->assertFalse($response->hasHeader('X-Drupal-Cache'));
   }