diff --git a/composer.json b/composer.json
index 049343a9ef..46cc81b28a 100644
--- a/composer.json
+++ b/composer.json
@@ -17,7 +17,7 @@
 		"squizlabs/php_codesniffer": "3.6.0",
 		"wp-coding-standards/wpcs": "~2.3.0",
 		"phpcompatibility/phpcompatibility-wp": "~2.1.3",
-		"yoast/phpunit-polyfills": "^1.0.1"
+		"yoast/phpunit-polyfills": "^1.1.0"
 	},
 	"config": {
 		"allow-plugins": {
diff --git a/tests/phpunit/includes/abstract-testcase.php b/tests/phpunit/includes/abstract-testcase.php
index f590642ef9..251d187a25 100644
--- a/tests/phpunit/includes/abstract-testcase.php
+++ b/tests/phpunit/includes/abstract-testcase.php
@@ -869,7 +869,7 @@ abstract class WP_UnitTestCase_Base extends PHPUnit_Adapter_TestCase {
 		$this->assertNotEmpty( $fields, $message . ' Fields array is empty.' );
 
 		foreach ( $fields as $field_name => $field_value ) {
-			$this->assertObjectHasAttribute( $field_name, $actual, $message . " Property $field_name does not exist on the object." );
+			$this->assertObjectHasProperty( $field_name, $actual, $message . " Property $field_name does not exist on the object." );
 			$this->assertSame( $field_value, $actual->$field_name, $message . " Value of property $field_name is not $field_value." );
 		}
 	}
diff --git a/tests/phpunit/includes/bootstrap.php b/tests/phpunit/includes/bootstrap.php
index 1113a87eea..96a84b33f8 100644
--- a/tests/phpunit/includes/bootstrap.php
+++ b/tests/phpunit/includes/bootstrap.php
@@ -139,7 +139,7 @@ unset( $phpunit_polyfills_autoloader, $phpunit_polyfills_error, $phpunit_polyfil
  * Minimum version of the PHPUnit Polyfills package as declared in `composer.json`.
  * Only needs updating when new polyfill features start being used in the test suite.
  */
-$phpunit_polyfills_minimum_version = '1.0.1';
+$phpunit_polyfills_minimum_version = '1.1.0';
 if ( class_exists( '\Yoast\PHPUnitPolyfills\Autoload' )
 	&& ( defined( '\Yoast\PHPUnitPolyfills\Autoload::VERSION' ) === false
 	|| version_compare( Yoast\PHPUnitPolyfills\Autoload::VERSION, $phpunit_polyfills_minimum_version, '<' ) )
diff --git a/tests/phpunit/includes/phpunit-adapter-testcase.php b/tests/phpunit/includes/phpunit-adapter-testcase.php
index 423a9d2213..13ac7bdd06 100644
--- a/tests/phpunit/includes/phpunit-adapter-testcase.php
+++ b/tests/phpunit/includes/phpunit-adapter-testcase.php
@@ -6,7 +6,7 @@ use Yoast\PHPUnitPolyfills\TestCases\TestCase as Polyfill_TestCase;
  * PHPUnit adapter layer.
  *
  * This class enhances the PHPUnit native `TestCase` with polyfills
- * for assertions and expectation methods added between PHPUnit 4.8 - 9.5.
+ * for assertions and expectation methods added between PHPUnit 4.8 - 9.6.
  *
  * Additionally, the Polyfill TestCase offers a workaround for the addition
  * of the `void` return type to PHPUnit fixture methods by providing
diff --git a/tests/phpunit/tests/ajax/wpAjaxImageEditor.php b/tests/phpunit/tests/ajax/wpAjaxImageEditor.php
index a06afa1f5c..ac761c3520 100644
--- a/tests/phpunit/tests/ajax/wpAjaxImageEditor.php
+++ b/tests/phpunit/tests/ajax/wpAjaxImageEditor.php
@@ -51,7 +51,7 @@ class Tests_Ajax_wpAjaxImageEditor extends WP_Ajax_UnitTestCase {
 
 		$ret = wp_save_image( $id );
 
-		$this->assertObjectHasAttribute( 'error', $ret );
+		$this->assertObjectHasProperty( 'error', $ret );
 		$this->assertEquals( 'Images cannot be scaled to a size larger than the original.', $ret->error );
 	}
 
diff --git a/tests/phpunit/tests/blocks/register.php b/tests/phpunit/tests/blocks/register.php
index f3617f5fad..0a5047c6d1 100644
--- a/tests/phpunit/tests/blocks/register.php
+++ b/tests/phpunit/tests/blocks/register.php
@@ -720,7 +720,7 @@ class Tests_Blocks_Register extends WP_UnitTestCase {
 
 		$registry   = WP_Block_Type_Registry::get_instance();
 		$block_type = $registry->get_registered( 'core/test-static' );
-		$this->assertObjectHasAttribute( 'editor_script_handles', $block_type );
+		$this->assertObjectHasProperty( 'editor_script_handles', $block_type );
 		$actual_script         = $block_type->editor_script;
 		$actual_script_handles = $block_type->editor_script_handles;
 
@@ -786,7 +786,7 @@ class Tests_Blocks_Register extends WP_UnitTestCase {
 
 		$registry   = WP_Block_Type_Registry::get_instance();
 		$block_type = $registry->get_registered( 'core/test-static' );
-		$this->assertObjectHasAttribute( 'editor_script_handles', $block_type );
+		$this->assertObjectHasProperty( 'editor_script_handles', $block_type );
 		$actual_script         = $block_type->editor_script;
 		$actual_script_handles = $block_type->editor_script_handles;
 
diff --git a/tests/phpunit/tests/comment.php b/tests/phpunit/tests/comment.php
index e3c6397b69..5be490107f 100644
--- a/tests/phpunit/tests/comment.php
+++ b/tests/phpunit/tests/comment.php
@@ -481,7 +481,7 @@ class Tests_Comment extends WP_UnitTestCase {
 			'The comment is not an instance of WP_Comment.'
 		);
 
-		$this->assertObjectHasAttribute(
+		$this->assertObjectHasProperty(
 			'comment_author',
 			$comment,
 			'The comment object does not have a "comment_author" property.'
diff --git a/tests/phpunit/tests/customize/manager.php b/tests/phpunit/tests/customize/manager.php
index f9b9b49cec..d42133a1ba 100644
--- a/tests/phpunit/tests/customize/manager.php
+++ b/tests/phpunit/tests/customize/manager.php
@@ -3339,14 +3339,14 @@ class Tests_WP_Customize_Manager extends WP_UnitTestCase {
 		$setting_id = 'dynamic';
 		$setting    = $manager->add_setting( $setting_id );
 		$this->assertSame( 'WP_Customize_Setting', get_class( $setting ) );
-		$this->assertObjectNotHasAttribute( 'custom', $setting );
+		$this->assertObjectNotHasProperty( 'custom', $setting );
 		$manager->remove_setting( $setting_id );
 
 		add_filter( 'customize_dynamic_setting_class', array( $this, 'return_dynamic_customize_setting_class' ), 10, 3 );
 		add_filter( 'customize_dynamic_setting_args', array( $this, 'return_dynamic_customize_setting_args' ), 10, 2 );
 		$setting = $manager->add_setting( $setting_id );
 		$this->assertSame( 'Test_Dynamic_Customize_Setting', get_class( $setting ) );
-		$this->assertObjectHasAttribute( 'custom', $setting );
+		$this->assertObjectHasProperty( 'custom', $setting );
 		$this->assertSame( 'foo', $setting->custom );
 	}
 
diff --git a/tests/phpunit/tests/customize/nav-menu-item-setting.php b/tests/phpunit/tests/customize/nav-menu-item-setting.php
index 256e5f577c..22d4bc7de7 100644
--- a/tests/phpunit/tests/customize/nav-menu-item-setting.php
+++ b/tests/phpunit/tests/customize/nav-menu-item-setting.php
@@ -926,17 +926,17 @@ class Test_WP_Customize_Nav_Menu_Item_Setting extends WP_UnitTestCase {
 		$nav_menu_item = $setting->value_as_wp_post_nav_menu_item();
 		$this->assertSame( 'Custom Label', $nav_menu_item->type_label );
 
-		$this->assertObjectNotHasAttribute( 'nav_menu_term_id', $nav_menu_item );
-		$this->assertObjectNotHasAttribute( 'status', $nav_menu_item );
+		$this->assertObjectNotHasProperty( 'nav_menu_term_id', $nav_menu_item );
+		$this->assertObjectNotHasProperty( 'status', $nav_menu_item );
 		$this->assertSame( 'publish', $nav_menu_item->post_status );
 		$this->assertSame( 'nav_menu_item', $nav_menu_item->post_type );
-		$this->assertObjectNotHasAttribute( 'position', $nav_menu_item );
+		$this->assertObjectNotHasProperty( 'position', $nav_menu_item );
 		$this->assertSame( $post_value['position'], $nav_menu_item->menu_order );
 		$this->assertSame( $post_value['title'], $nav_menu_item->post_title );
 		$this->assertSame( 123, $nav_menu_item->ID );
 		$this->assertSame( 123, $nav_menu_item->db_id );
 		$this->assertSame( wp_get_current_user()->ID, $nav_menu_item->post_author );
-		$this->assertObjectHasAttribute( 'type_label', $nav_menu_item );
+		$this->assertObjectHasProperty( 'type_label', $nav_menu_item );
 		$expected = apply_filters( 'nav_menu_attr_title', wp_unslash( apply_filters( 'excerpt_save_pre', wp_slash( $post_value['attr_title'] ) ) ) );
 		$this->assertSame( $expected, $nav_menu_item->attr_title );
 		$this->assertSame( 'Attempted \o/ o&#8217;o markup', $nav_menu_item->description );
@@ -1070,7 +1070,7 @@ class Test_WP_Customize_Nav_Menu_Item_Setting extends WP_UnitTestCase {
 		$this->assertSame( $original_post_title, $item_value['original_title'] );
 		$this->assertSame( '', $item_value['title'] );
 		$item = $setting->value_as_wp_post_nav_menu_item();
-		$this->assertObjectHasAttribute( 'type_label', $item );
+		$this->assertObjectHasProperty( 'type_label', $item );
 		$this->assertSame( $original_post_title, $item->original_title );
 		$this->assertSame( $original_post_title, $item->title );
 		$this->assertArrayHasKey( 'type_label', $item_value );
@@ -1097,7 +1097,7 @@ class Test_WP_Customize_Nav_Menu_Item_Setting extends WP_UnitTestCase {
 		$this->assertSame( $original_post_title, $item_value['original_title'] );
 		$this->assertSame( '', $item_value['title'] );
 		$item = $setting->value_as_wp_post_nav_menu_item();
-		$this->assertObjectHasAttribute( 'type_label', $item );
+		$this->assertObjectHasProperty( 'type_label', $item );
 		$this->assertSame( $original_post_title, $item->original_title );
 		$this->assertSame( $original_post_title, $item->title );
 		$this->assertArrayHasKey( 'type_label', $item_value );
@@ -1124,7 +1124,7 @@ class Test_WP_Customize_Nav_Menu_Item_Setting extends WP_UnitTestCase {
 		$this->assertSame( $original_term_title, $item_value['original_title'] );
 		$this->assertSame( '', $item_value['title'] );
 		$item = $setting->value_as_wp_post_nav_menu_item();
-		$this->assertObjectHasAttribute( 'type_label', $item );
+		$this->assertObjectHasProperty( 'type_label', $item );
 		$this->assertSame( $original_term_title, $item->original_title );
 		$this->assertSame( $original_term_title, $item->title );
 		$this->assertArrayHasKey( 'type_label', $item_value );
@@ -1151,7 +1151,7 @@ class Test_WP_Customize_Nav_Menu_Item_Setting extends WP_UnitTestCase {
 		$this->assertSame( $original_term_title, $item_value['original_title'] );
 		$this->assertSame( '', $item_value['title'] );
 		$item = $setting->value_as_wp_post_nav_menu_item();
-		$this->assertObjectHasAttribute( 'type_label', $item );
+		$this->assertObjectHasProperty( 'type_label', $item );
 		$this->assertSame( $original_term_title, $item->original_title );
 		$this->assertSame( $original_term_title, $item->title );
 		$this->assertArrayHasKey( 'type_label', $item_value );
@@ -1177,7 +1177,7 @@ class Test_WP_Customize_Nav_Menu_Item_Setting extends WP_UnitTestCase {
 		$this->assertSame( get_post_type_object( 'press_release' )->labels->archives, $item_value['original_title'] );
 		$this->assertSame( '', $item_value['title'] );
 		$item = $setting->value_as_wp_post_nav_menu_item();
-		$this->assertObjectHasAttribute( 'type_label', $item );
+		$this->assertObjectHasProperty( 'type_label', $item );
 		$this->assertSame( get_post_type_object( 'press_release' )->labels->archives, $item->original_title );
 		$this->assertSame( get_post_type_object( 'press_release' )->labels->archives, $item->title );
 		$this->assertArrayHasKey( 'type_label', $item_value );
@@ -1203,7 +1203,7 @@ class Test_WP_Customize_Nav_Menu_Item_Setting extends WP_UnitTestCase {
 		$this->assertSame( get_post_type_object( 'press_release' )->labels->archives, $item_value['original_title'] );
 		$this->assertSame( '', $item_value['title'] );
 		$item = $setting->value_as_wp_post_nav_menu_item();
-		$this->assertObjectHasAttribute( 'type_label', $item );
+		$this->assertObjectHasProperty( 'type_label', $item );
 		$this->assertSame( get_post_type_object( 'press_release' )->labels->archives, $item->original_title );
 		$this->assertSame( get_post_type_object( 'press_release' )->labels->archives, $item->title );
 		$this->assertArrayHasKey( 'type_label', $item_value );
diff --git a/tests/phpunit/tests/post.php b/tests/phpunit/tests/post.php
index e895dd9e76..548c5eb2ca 100644
--- a/tests/phpunit/tests/post.php
+++ b/tests/phpunit/tests/post.php
@@ -236,7 +236,7 @@ class Tests_Post extends WP_UnitTestCase {
 		register_post_status( 'test' );
 
 		$counts = wp_count_posts();
-		$this->assertObjectHasAttribute( 'test', $counts );
+		$this->assertObjectHasProperty( 'test', $counts );
 		$this->assertSame( 0, $counts->test );
 	}
 
diff --git a/tests/phpunit/tests/post/getPostTypeLabels.php b/tests/phpunit/tests/post/getPostTypeLabels.php
index 9761e419b0..2a0e7f0d32 100644
--- a/tests/phpunit/tests/post/getPostTypeLabels.php
+++ b/tests/phpunit/tests/post/getPostTypeLabels.php
@@ -95,9 +95,9 @@ class Tests_Post_GetPostTypeLabels extends WP_UnitTestCase {
 
 		unregister_post_type( 'foo' );
 
-		$this->assertObjectHasAttribute( 'labels', $post_type_object );
-		$this->assertObjectHasAttribute( 'label', $post_type_object );
-		$this->assertObjectHasAttribute( 'not_found_in_trash', $post_type_object->labels );
+		$this->assertObjectHasProperty( 'labels', $post_type_object );
+		$this->assertObjectHasProperty( 'label', $post_type_object );
+		$this->assertObjectHasProperty( 'not_found_in_trash', $post_type_object->labels );
 	}
 
 	public function test_label_should_be_derived_from_labels_when_registering_a_post_type() {
@@ -122,8 +122,8 @@ class Tests_Post_GetPostTypeLabels extends WP_UnitTestCase {
 		add_filter( 'post_type_labels_foo', array( $this, 'filter_post_type_labels' ) );
 		register_post_type( 'foo' );
 
-		$this->assertObjectHasAttribute( 'featured_image', get_post_type_object( 'foo' )->labels );
-		$this->assertObjectHasAttribute( 'set_featured_image', get_post_type_object( 'foo' )->labels );
+		$this->assertObjectHasProperty( 'featured_image', get_post_type_object( 'foo' )->labels );
+		$this->assertObjectHasProperty( 'set_featured_image', get_post_type_object( 'foo' )->labels );
 
 		unregister_post_type( 'foo' );
 		remove_filter( 'post_type_labels_foo', array( $this, 'filter_post_type_labels' ) );
diff --git a/tests/phpunit/tests/post/updatePostCache.php b/tests/phpunit/tests/post/updatePostCache.php
index cfb279b67c..9427ec6fbd 100644
--- a/tests/phpunit/tests/post/updatePostCache.php
+++ b/tests/phpunit/tests/post/updatePostCache.php
@@ -57,7 +57,7 @@ class Tests_Post_UpdatePostCache extends WP_UnitTestCase {
 			'The cached post is not an object'
 		);
 
-		$this->assertObjectHasAttribute(
+		$this->assertObjectHasProperty(
 			'filter',
 			$cached_post,
 			'The cached post does not have a "filter" property'
@@ -98,7 +98,7 @@ class Tests_Post_UpdatePostCache extends WP_UnitTestCase {
 			'The cached post is not an object'
 		);
 
-		$this->assertObjectHasAttribute(
+		$this->assertObjectHasProperty(
 			'filter',
 			$cached_post,
 			'The cached post does not have a "filter" property'
@@ -126,7 +126,7 @@ class Tests_Post_UpdatePostCache extends WP_UnitTestCase {
 			'The cached post is not an object'
 		);
 
-		$this->assertObjectHasAttribute(
+		$this->assertObjectHasProperty(
 			'filter',
 			$cached_post,
 			'The cached post does not have a "filter" property'
diff --git a/tests/phpunit/tests/rest-api/rest-server.php b/tests/phpunit/tests/rest-api/rest-server.php
index 9a12c2247b..b752b83872 100644
--- a/tests/phpunit/tests/rest-api/rest-server.php
+++ b/tests/phpunit/tests/rest-api/rest-server.php
@@ -1261,7 +1261,7 @@ class Tests_REST_Server extends WP_Test_REST_TestCase {
 
 		$result = json_decode( rest_get_server()->sent_body );
 
-		$this->assertObjectNotHasAttribute( 'code', $result );
+		$this->assertObjectNotHasProperty( 'code', $result );
 	}
 
 	public function test_link_header_on_requests() {
diff --git a/tests/phpunit/tests/rest-api/wpRestTemplatesController.php b/tests/phpunit/tests/rest-api/wpRestTemplatesController.php
index f7f6bed9c5..266ca89a33 100644
--- a/tests/phpunit/tests/rest-api/wpRestTemplatesController.php
+++ b/tests/phpunit/tests/rest-api/wpRestTemplatesController.php
@@ -870,13 +870,13 @@ class Tests_REST_WpRestTemplatesController extends WP_Test_REST_Controller_Testc
 
 		$this->assertInstanceOf( 'stdClass', $prepared, 'The item could not be prepared for the database.' );
 
-		$this->assertObjectHasAttribute( 'post_type', $prepared, 'The "post_type" was not included in the prepared template part.' );
-		$this->assertObjectHasAttribute( 'post_status', $prepared, 'The "post_status" was not included in the prepared template part.' );
-		$this->assertObjectHasAttribute( 'tax_input', $prepared, 'The "tax_input" was not included in the prepared template part.' );
+		$this->assertObjectHasProperty( 'post_type', $prepared, 'The "post_type" was not included in the prepared template part.' );
+		$this->assertObjectHasProperty( 'post_status', $prepared, 'The "post_status" was not included in the prepared template part.' );
+		$this->assertObjectHasProperty( 'tax_input', $prepared, 'The "tax_input" was not included in the prepared template part.' );
 		$this->assertArrayHasKey( 'wp_theme', $prepared->tax_input, 'The "wp_theme" tax was not included in the prepared template part.' );
 		$this->assertArrayHasKey( 'wp_template_part_area', $prepared->tax_input, 'The "wp_template_part_area" tax was not included in the prepared template part.' );
-		$this->assertObjectHasAttribute( 'post_content', $prepared, 'The "post_content" was not included in the prepared template part.' );
-		$this->assertObjectHasAttribute( 'post_title', $prepared, 'The "post_title" was not included in the prepared template part.' );
+		$this->assertObjectHasProperty( 'post_content', $prepared, 'The "post_content" was not included in the prepared template part.' );
+		$this->assertObjectHasProperty( 'post_title', $prepared, 'The "post_title" was not included in the prepared template part.' );
 
 		$this->assertSame( 'wp_template_part', $prepared->post_type, 'The "post_type" in the prepared template part should be "wp_template_part".' );
 		$this->assertSame( 'publish', $prepared->post_status, 'The post status in the prepared template part should be "publish".' );
diff --git a/tests/phpunit/tests/taxonomy.php b/tests/phpunit/tests/taxonomy.php
index 9b31b573a2..ce04e22a1b 100644
--- a/tests/phpunit/tests/taxonomy.php
+++ b/tests/phpunit/tests/taxonomy.php
@@ -284,7 +284,7 @@ class Tests_Taxonomy extends WP_UnitTestCase {
 		// Create a post type to test with.
 		$post_type = 'test_cpt';
 		$this->assertFalse( get_post_type( $post_type ) );
-		$this->assertObjectHasAttribute( 'name', register_post_type( $post_type ) );
+		$this->assertObjectHasProperty( 'name', register_post_type( $post_type ) );
 
 		// Core taxonomy, core post type.
 		$this->assertTrue( unregister_taxonomy_for_object_type( 'category', 'post' ) );
diff --git a/tests/phpunit/tests/term/query.php b/tests/phpunit/tests/term/query.php
index 8a7e6e91eb..0e118a3c16 100644
--- a/tests/phpunit/tests/term/query.php
+++ b/tests/phpunit/tests/term/query.php
@@ -402,7 +402,7 @@ class Tests_Term_Query extends WP_UnitTestCase {
 		$this->assertNotEmpty( $terms );
 		foreach ( $terms as $term ) {
 			$this->assertInstanceOf( 'WP_Term', $term );
-			$this->assertObjectHasAttribute( 'object_id', $term );
+			$this->assertObjectHasProperty( 'object_id', $term );
 		}
 
 		// Run again to check the cached response.
@@ -410,7 +410,7 @@ class Tests_Term_Query extends WP_UnitTestCase {
 		$this->assertNotEmpty( $terms );
 		foreach ( $terms as $term ) {
 			$this->assertInstanceOf( 'WP_Term', $term );
-			$this->assertObjectHasAttribute( 'object_id', $term );
+			$this->assertObjectHasProperty( 'object_id', $term );
 		}
 	}
 
diff --git a/tests/phpunit/tests/term/wpGetObjectTerms.php b/tests/phpunit/tests/term/wpGetObjectTerms.php
index 5c0faec53b..948ba1e1c3 100644
--- a/tests/phpunit/tests/term/wpGetObjectTerms.php
+++ b/tests/phpunit/tests/term/wpGetObjectTerms.php
@@ -850,7 +850,7 @@ class Tests_Term_WpGetObjectTerms extends WP_UnitTestCase {
 		}
 
 		$term = get_term( $t );
-		$this->assertObjectNotHasAttribute( 'object_id', $term );
+		$this->assertObjectNotHasProperty( 'object_id', $term );
 	}
 
 	/**
diff --git a/tests/phpunit/tests/user/multisite.php b/tests/phpunit/tests/user/multisite.php
index 23079f4799..e3173db43e 100644
--- a/tests/phpunit/tests/user/multisite.php
+++ b/tests/phpunit/tests/user/multisite.php
@@ -59,15 +59,15 @@ if ( is_multisite() ) :
 			// Each site retrieved should match the expected structure.
 			foreach ( $blogs_of_user as $blog_id => $blog ) {
 				$this->assertSame( $blog_id, $blog->userblog_id );
-				$this->assertObjectHasAttribute( 'userblog_id', $blog );
-				$this->assertObjectHasAttribute( 'blogname', $blog );
-				$this->assertObjectHasAttribute( 'domain', $blog );
-				$this->assertObjectHasAttribute( 'path', $blog );
-				$this->assertObjectHasAttribute( 'site_id', $blog );
-				$this->assertObjectHasAttribute( 'siteurl', $blog );
-				$this->assertObjectHasAttribute( 'archived', $blog );
-				$this->assertObjectHasAttribute( 'spam', $blog );
-				$this->assertObjectHasAttribute( 'deleted', $blog );
+				$this->assertObjectHasProperty( 'userblog_id', $blog );
+				$this->assertObjectHasProperty( 'blogname', $blog );
+				$this->assertObjectHasProperty( 'domain', $blog );
+				$this->assertObjectHasProperty( 'path', $blog );
+				$this->assertObjectHasProperty( 'site_id', $blog );
+				$this->assertObjectHasProperty( 'siteurl', $blog );
+				$this->assertObjectHasProperty( 'archived', $blog );
+				$this->assertObjectHasProperty( 'spam', $blog );
+				$this->assertObjectHasProperty( 'deleted', $blog );
 			}
 
 			// Mark each remaining site as spam, archived, and deleted.