diff --git a/phpunit/block-template-utils-test.php b/phpunit/block-template-utils-test.php
index ac2e4145cd0ed..08fb0c2c2c1e3 100644
--- a/phpunit/block-template-utils-test.php
+++ b/phpunit/block-template-utils-test.php
@@ -9,9 +9,6 @@ class Tests_Block_Template_Utils extends WP_UnitTestCase {
 	public function set_up() {
 		parent::set_up();
 		switch_theme( 'emptytheme' );
-	}
-
-	public static function wpSetUpBeforeClass() {
 		register_post_type(
 			'custom_book',
 			array(
@@ -22,9 +19,10 @@ public static function wpSetUpBeforeClass() {
 		register_taxonomy( 'book_type', 'custom_book' );
 	}
 
-	public static function wpTearDownAfterClass() {
+	public function tear_down() {
 		unregister_post_type( 'custom_book' );
 		unregister_taxonomy( 'book_type' );
+		parent::tear_down();
 	}
 
 	public function test_get_template_hierarchy() {
diff --git a/phpunit/bootstrap.php b/phpunit/bootstrap.php
index c11233b1e8952..f64e6fa5c7ef1 100644
--- a/phpunit/bootstrap.php
+++ b/phpunit/bootstrap.php
@@ -22,6 +22,12 @@
 	define( 'LOCAL_WP_ENVIRONMENT_TYPE', 'local' );
 }
 
+// Pretend that these are Core unit tests. This is needed so that
+// wp_theme_has_theme_json() does not cache its return value between each test.
+if ( ! defined( 'WP_RUN_CORE_TESTS' ) ) {
+	define( 'WP_RUN_CORE_TESTS', true );
+}
+
 // Require composer dependencies.
 require_once dirname( __DIR__ ) . '/vendor/autoload.php';