diff --git a/composer.lock b/composer.lock
index f6bbedd9806d37513f9a8c2c2fffd588076efc19..400480d33b9ff5711af75ecddecc0252838c3f2a 100644
--- a/composer.lock
+++ b/composer.lock
@@ -6547,16 +6547,16 @@
         },
         {
             "name": "phpunit/phpunit",
-            "version": "9.5.28",
+            "version": "9.6.7",
             "source": {
                 "type": "git",
                 "url": "https://github.com/sebastianbergmann/phpunit.git",
-                "reference": "954ca3113a03bf780d22f07bf055d883ee04b65e"
+                "reference": "c993f0d3b0489ffc42ee2fe0bd645af1538a63b2"
             },
             "dist": {
                 "type": "zip",
-                "url": "https://api.github.com/repos/sebastianbergmann/phpunit/zipball/954ca3113a03bf780d22f07bf055d883ee04b65e",
-                "reference": "954ca3113a03bf780d22f07bf055d883ee04b65e",
+                "url": "https://api.github.com/repos/sebastianbergmann/phpunit/zipball/c993f0d3b0489ffc42ee2fe0bd645af1538a63b2",
+                "reference": "c993f0d3b0489ffc42ee2fe0bd645af1538a63b2",
                 "shasum": ""
             },
             "require": {
@@ -6589,8 +6589,8 @@
                 "sebastian/version": "^3.0.2"
             },
             "suggest": {
-                "ext-soap": "*",
-                "ext-xdebug": "*"
+                "ext-soap": "To be able to generate mocks based on WSDL files",
+                "ext-xdebug": "PHP extension that provides line coverage as well as branch and path coverage"
             },
             "bin": [
                 "phpunit"
@@ -6598,7 +6598,7 @@
             "type": "library",
             "extra": {
                 "branch-alias": {
-                    "dev-master": "9.5-dev"
+                    "dev-master": "9.6-dev"
                 }
             },
             "autoload": {
@@ -6629,7 +6629,8 @@
             ],
             "support": {
                 "issues": "https://github.com/sebastianbergmann/phpunit/issues",
-                "source": "https://github.com/sebastianbergmann/phpunit/tree/9.5.28"
+                "security": "https://github.com/sebastianbergmann/phpunit/security/policy",
+                "source": "https://github.com/sebastianbergmann/phpunit/tree/9.6.7"
             },
             "funding": [
                 {
@@ -6645,7 +6646,7 @@
                     "type": "tidelift"
                 }
             ],
-            "time": "2023-01-14T12:32:24+00:00"
+            "time": "2023-04-14T08:58:40+00:00"
         },
         {
             "name": "react/promise",
diff --git a/composer/Metapackage/PinnedDevDependencies/composer.json b/composer/Metapackage/PinnedDevDependencies/composer.json
index dc06617ef890ace8c54f489b98372ad7309e87a4..a10758dc1507409ecfb1018f2f6f49a1639c085b 100644
--- a/composer/Metapackage/PinnedDevDependencies/composer.json
+++ b/composer/Metapackage/PinnedDevDependencies/composer.json
@@ -44,7 +44,7 @@
         "phpunit/php-invoker": "3.1.1",
         "phpunit/php-text-template": "2.0.4",
         "phpunit/php-timer": "5.0.3",
-        "phpunit/phpunit": "9.5.28",
+        "phpunit/phpunit": "9.6.7",
         "react/promise": "v2.9.0",
         "sebastian/cli-parser": "1.0.1",
         "sebastian/code-unit": "1.0.8",
diff --git a/core/.deprecation-ignore.txt b/core/.deprecation-ignore.txt
index ea8370ee740c2da8976126d3beaf9adc98978c3b..4a13e960cba72f666d92f6b0e9bd0cb80d229b6f 100644
--- a/core/.deprecation-ignore.txt
+++ b/core/.deprecation-ignore.txt
@@ -22,6 +22,12 @@
 %"PHPUnit\\Framework\\TestSuite".*is considered internal%
 %"PHPUnit\\TextUI\\DefaultResultPrinter".*is considered internal%
 
+# PHPUnit 9.6.
+%Expecting E_WARNING and E_USER_WARNING is deprecated and will no longer be possible in PHPUnit 10%
+%Expecting E_ERROR and E_USER_ERROR is deprecated and will no longer be possible in PHPUnit 10%
+%assertObjectHasAttribute\(\) is deprecated and will be removed in PHPUnit 10%
+%assertObjectNotHasAttribute\(\) is deprecated and will be removed in PHPUnit 10%
+
 # Skip deprecations for EditorMediaDialog, EditorImageDialog and EditorLinkDialog triggered by
 # \Drupal\Core\Entity\EntityResolverManager::setRouteOptions().
 %Drupal\\media\\Form\\EditorMediaDialog is deprecated in drupal:10.1.0 and is removed from drupal:11.0.0. There is no replacement. See https://www.drupal.org/project/drupal/issues/3291493%
diff --git a/core/tests/Drupal/Tests/Component/Diff/Engine/DiffOpTest.php b/core/tests/Drupal/Tests/Component/Diff/Engine/DiffOpTest.php
index a8c7ac72bafa309f590fe281bf75d7e1ed72e663..fa2dee1a029e47226ce7d892c68500bb6fe9660b 100644
--- a/core/tests/Drupal/Tests/Component/Diff/Engine/DiffOpTest.php
+++ b/core/tests/Drupal/Tests/Component/Diff/Engine/DiffOpTest.php
@@ -3,6 +3,7 @@
 namespace Drupal\Tests\Component\Diff\Engine;
 
 use Drupal\Component\Diff\Engine\DiffOp;
+use Drupal\Tests\Traits\PhpUnitWarnings;
 use PHPUnit\Framework\TestCase;
 use Symfony\Bridge\PhpUnit\ExpectDeprecationTrait;
 
@@ -21,6 +22,7 @@
 class DiffOpTest extends TestCase {
 
   use ExpectDeprecationTrait;
+  use PhpUnitWarnings;
 
   /**
    * DiffOp::reverse() always throws an error.
diff --git a/core/tests/Drupal/Tests/Traits/PhpUnitWarnings.php b/core/tests/Drupal/Tests/Traits/PhpUnitWarnings.php
index cdb3150f2e470b362201db1391ce5a74d8cd884c..9b92762e1b18ce315ee5911bcb0c3fadaeec4edc 100644
--- a/core/tests/Drupal/Tests/Traits/PhpUnitWarnings.php
+++ b/core/tests/Drupal/Tests/Traits/PhpUnitWarnings.php
@@ -33,6 +33,11 @@ trait PhpUnitWarnings {
     'assertDirectoryNotIsWritable() is deprecated and will be removed in PHPUnit 10. Refactor your code to use assertDirectoryIsNotWritable() instead.',
     'assertFileNotIsWritable() is deprecated and will be removed in PHPUnit 10. Refactor your code to use assertFileIsNotWritable() instead.',
     'The at() matcher has been deprecated. It will be removed in PHPUnit 10. Please refactor your test to not rely on the order in which methods are invoked.',
+    // PHPUnit 9.6.
+    'Expecting E_WARNING and E_USER_WARNING is deprecated and will no longer be possible in PHPUnit 10.',
+    'Expecting E_ERROR and E_USER_ERROR is deprecated and will no longer be possible in PHPUnit 10.',
+    'assertObjectHasAttribute() is deprecated and will be removed in PHPUnit 10. Refactor your test to use assertObjectHasProperty() (PHPUnit 10.1.0+) instead.',
+    'assertObjectNotHasAttribute() is deprecated and will be removed in PHPUnit 10. Refactor your test to use assertObjectNotHasProperty() (PHPUnit 10.1.0+) instead.',
   ];
 
   /**