diff --git a/src/wp-admin/includes/theme.php b/src/wp-admin/includes/theme.php
index 6bb450ee1b..ea73d8650d 100644
--- a/src/wp-admin/includes/theme.php
+++ b/src/wp-admin/includes/theme.php
@@ -1166,11 +1166,14 @@ function resume_theme( $theme, $redirect = '' ) {
 	 * creating a fatal error.
 	 */
 	if ( ! empty( $redirect ) ) {
+		$stylesheet_path = get_stylesheet_directory();
+		$template_path   = get_template_directory();
+
 		$functions_path = '';
-		if ( str_contains( STYLESHEETPATH, $extension ) ) {
-			$functions_path = STYLESHEETPATH . '/functions.php';
-		} elseif ( str_contains( TEMPLATEPATH, $extension ) ) {
-			$functions_path = TEMPLATEPATH . '/functions.php';
+		if ( str_contains( $stylesheet_path, $extension ) ) {
+			$functions_path = $stylesheet_path . '/functions.php';
+		} elseif ( str_contains( $template_path, $extension ) ) {
+			$functions_path = $template_path . '/functions.php';
 		}
 
 		if ( ! empty( $functions_path ) ) {
diff --git a/src/wp-includes/comment-template.php b/src/wp-includes/comment-template.php
index 03f450dc9b..a80dc60e41 100644
--- a/src/wp-includes/comment-template.php
+++ b/src/wp-includes/comment-template.php
@@ -1381,7 +1381,7 @@ function wp_comment_form_unfiltered_html_nonce() {
  * and the post ID respectively.
  *
  * The `$file` path is passed through a filter hook called {@see 'comments_template'},
- * which includes the TEMPLATEPATH and $file combined. Tries the $filtered path
+ * which includes the template directory and $file combined. Tries the $filtered path
  * first and if it fails it will require the default comment template from the
  * default theme. If either does not exist, then the WordPress process will be
  * halted. It is advised for that reason, that the default theme is not deleted.
@@ -1600,7 +1600,10 @@ function comments_template( $file = '/comments.php', $separate_comments = false
 		define( 'COMMENTS_TEMPLATE', true );
 	}
 
-	$theme_template = STYLESHEETPATH . $file;
+	$stylesheet_path = get_stylesheet_directory();
+	$template_path   = get_template_directory();
+
+	$theme_template = $stylesheet_path . $file;
 
 	/**
 	 * Filters the path to the theme template file used for the comments template.
@@ -1613,8 +1616,8 @@ function comments_template( $file = '/comments.php', $separate_comments = false
 
 	if ( file_exists( $include ) ) {
 		require $include;
-	} elseif ( file_exists( TEMPLATEPATH . $file ) ) {
-		require TEMPLATEPATH . $file;
+	} elseif ( file_exists( $template_path . $file ) ) {
+		require $template_path . $file;
 	} else { // Backward compat code will be removed in a future release.
 		require ABSPATH . WPINC . '/theme-compat/comments.php';
 	}
diff --git a/src/wp-includes/default-constants.php b/src/wp-includes/default-constants.php
index 6e64e789a0..0c0ee771eb 100644
--- a/src/wp-includes/default-constants.php
+++ b/src/wp-includes/default-constants.php
@@ -407,6 +407,8 @@ function wp_templating_constants() {
 	 * Filesystem path to the current active template directory.
 	 *
 	 * @since 1.5.0
+	 * @deprecated 6.4.0 Use get_template_directory() instead.
+	 * @see get_template_directory()
 	 */
 	define( 'TEMPLATEPATH', get_template_directory() );
 
@@ -414,6 +416,8 @@ function wp_templating_constants() {
 	 * Filesystem path to the current active template stylesheet directory.
 	 *
 	 * @since 2.1.0
+	 * @deprecated 6.4.0 Use get_stylesheet_directory() instead.
+	 * @see get_stylesheet_directory()
 	 */
 	define( 'STYLESHEETPATH', get_stylesheet_directory() );
 
diff --git a/src/wp-includes/load.php b/src/wp-includes/load.php
index 8f18a3a6e9..77e17b3f8b 100644
--- a/src/wp-includes/load.php
+++ b/src/wp-includes/load.php
@@ -1049,11 +1049,14 @@ function wp_get_active_and_valid_themes() {
 		return $themes;
 	}
 
-	if ( TEMPLATEPATH !== STYLESHEETPATH ) {
-		$themes[] = STYLESHEETPATH;
+	$stylesheet_path = get_stylesheet_directory();
+	$template_path   = get_template_directory();
+
+	if ( $template_path !== $stylesheet_path ) {
+		$themes[] = $stylesheet_path;
 	}
 
-	$themes[] = TEMPLATEPATH;
+	$themes[] = $template_path;
 
 	/*
 	 * Remove themes from the list of active themes when we're on an endpoint
diff --git a/src/wp-includes/template.php b/src/wp-includes/template.php
index afc2ca6edf..989d630f7f 100644
--- a/src/wp-includes/template.php
+++ b/src/wp-includes/template.php
@@ -684,8 +684,9 @@ function get_attachment_template() {
 /**
  * Retrieves the name of the highest priority template file that exists.
  *
- * Searches in the STYLESHEETPATH before TEMPLATEPATH and wp-includes/theme-compat
- * so that themes which inherit from a parent theme can just overload one file.
+ * Searches in the stylesheet directory before the template directory and
+ * wp-includes/theme-compat so that themes which inherit from a parent theme
+ * can just overload one file.
  *
  * @since 2.7.0
  * @since 5.5.0 The `$args` parameter was added.
@@ -699,16 +700,20 @@ function get_attachment_template() {
  * @return string The template filename if one is located.
  */
 function locate_template( $template_names, $load = false, $load_once = true, $args = array() ) {
+	$stylesheet_path = get_stylesheet_directory();
+	$template_path   = get_template_directory();
+	$is_child_theme  = $stylesheet_path !== $template_path;
+
 	$located = '';
 	foreach ( (array) $template_names as $template_name ) {
 		if ( ! $template_name ) {
 			continue;
 		}
-		if ( file_exists( STYLESHEETPATH . '/' . $template_name ) ) {
-			$located = STYLESHEETPATH . '/' . $template_name;
+		if ( file_exists( $stylesheet_path . '/' . $template_name ) ) {
+			$located = $stylesheet_path . '/' . $template_name;
 			break;
-		} elseif ( is_child_theme() && file_exists( TEMPLATEPATH . '/' . $template_name ) ) {
-			$located = TEMPLATEPATH . '/' . $template_name;
+		} elseif ( $is_child_theme && file_exists( $template_path . '/' . $template_name ) ) {
+			$located = $template_path . '/' . $template_name;
 			break;
 		} elseif ( file_exists( ABSPATH . WPINC . '/theme-compat/' . $template_name ) ) {
 			$located = ABSPATH . WPINC . '/theme-compat/' . $template_name;
diff --git a/src/wp-includes/theme.php b/src/wp-includes/theme.php
index 5ff31953b1..6be2ad700a 100644
--- a/src/wp-includes/theme.php
+++ b/src/wp-includes/theme.php
@@ -157,7 +157,7 @@ function wp_clean_themes_cache( $clear_update_cache = true ) {
  * @return bool True if a child theme is in use, false otherwise.
  */
 function is_child_theme() {
-	return ( TEMPLATEPATH !== STYLESHEETPATH );
+	return get_template_directory() !== get_stylesheet_directory();
 }
 
 /**
@@ -187,24 +187,40 @@ function get_stylesheet() {
  * Retrieves stylesheet directory path for the active theme.
  *
  * @since 1.5.0
+ * @since 6.4.0 Memoizes filter execution so that it only runs once for the current theme.
+ *
+ * @global string $wp_stylesheet_path Current theme stylesheet directory path.
  *
  * @return string Path to active theme's stylesheet directory.
  */
 function get_stylesheet_directory() {
-	$stylesheet     = get_stylesheet();
-	$theme_root     = get_theme_root( $stylesheet );
-	$stylesheet_dir = "$theme_root/$stylesheet";
+	global $wp_stylesheet_path;
 
-	/**
-	 * Filters the stylesheet directory path for the active theme.
-	 *
-	 * @since 1.5.0
-	 *
-	 * @param string $stylesheet_dir Absolute path to the active theme.
-	 * @param string $stylesheet     Directory name of the active theme.
-	 * @param string $theme_root     Absolute path to themes directory.
-	 */
-	return apply_filters( 'stylesheet_directory', $stylesheet_dir, $stylesheet, $theme_root );
+	if ( null === $wp_stylesheet_path ) {
+		$stylesheet     = get_stylesheet();
+		$theme_root     = get_theme_root( $stylesheet );
+		$stylesheet_dir = "$theme_root/$stylesheet";
+
+		/**
+		 * Filters the stylesheet directory path for the active theme.
+		 *
+		 * @since 1.5.0
+		 *
+		 * @param string $stylesheet_dir Absolute path to the active theme.
+		 * @param string $stylesheet     Directory name of the active theme.
+		 * @param string $theme_root     Absolute path to themes directory.
+		 */
+		$stylesheet_dir = apply_filters( 'stylesheet_directory', $stylesheet_dir, $stylesheet, $theme_root );
+
+		// If there are filter callbacks, force the logic to execute on every call.
+		if ( has_filter( 'stylesheet' ) || has_filter( 'theme_root' ) || has_filter( 'stylesheet_directory' ) ) {
+			return $stylesheet_dir;
+		}
+
+		$wp_stylesheet_path = $stylesheet_dir;
+	}
+
+	return $wp_stylesheet_path;
 }
 
 /**
@@ -321,24 +337,40 @@ function get_template() {
  * Retrieves template directory path for the active theme.
  *
  * @since 1.5.0
+ * @since 6.4.0 Memoizes filter execution so that it only runs once for the current theme.
+ *
+ * @global string $wp_template_path Current theme template directory path.
  *
  * @return string Path to active theme's template directory.
  */
 function get_template_directory() {
-	$template     = get_template();
-	$theme_root   = get_theme_root( $template );
-	$template_dir = "$theme_root/$template";
+	global $wp_template_path;
 
-	/**
-	 * Filters the active theme directory path.
-	 *
-	 * @since 1.5.0
-	 *
-	 * @param string $template_dir The path of the active theme directory.
-	 * @param string $template     Directory name of the active theme.
-	 * @param string $theme_root   Absolute path to the themes directory.
-	 */
-	return apply_filters( 'template_directory', $template_dir, $template, $theme_root );
+	if ( null === $wp_template_path ) {
+		$template     = get_template();
+		$theme_root   = get_theme_root( $template );
+		$template_dir = "$theme_root/$template";
+
+		/**
+		 * Filters the active theme directory path.
+		 *
+		 * @since 1.5.0
+		 *
+		 * @param string $template_dir The path of the active theme directory.
+		 * @param string $template     Directory name of the active theme.
+		 * @param string $theme_root   Absolute path to the themes directory.
+		 */
+		$template_dir = apply_filters( 'template_directory', $template_dir, $template, $theme_root );
+
+		// If there are filter callbacks, force the logic to execute on every call.
+		if ( has_filter( 'template' ) || has_filter( 'theme_root' ) || has_filter( 'template_directory' ) ) {
+			return $template_dir;
+		}
+
+		$wp_template_path = $template_dir;
+	}
+
+	return $wp_template_path;
 }
 
 /**
@@ -744,11 +776,13 @@ function locale_stylesheet() {
  * @global WP_Customize_Manager $wp_customize
  * @global array                $sidebars_widgets
  * @global array                $wp_registered_sidebars
+ * @global string               $wp_stylesheet_path
+ * @global string               $wp_template_path
  *
  * @param string $stylesheet Stylesheet name.
  */
 function switch_theme( $stylesheet ) {
-	global $wp_theme_directories, $wp_customize, $sidebars_widgets, $wp_registered_sidebars;
+	global $wp_theme_directories, $wp_customize, $sidebars_widgets, $wp_registered_sidebars, $wp_stylesheet_path, $wp_template_path;
 
 	$requirements = validate_theme_requirements( $stylesheet );
 	if ( is_wp_error( $requirements ) ) {
@@ -832,6 +866,13 @@ function switch_theme( $stylesheet ) {
 
 	update_option( 'theme_switched', $old_theme->get_stylesheet() );
 
+	/*
+	 * Reset globals to force refresh the next time these directories are
+	 * accessed via `get_stylesheet_directory()` / `get_template_directory()`.
+	 */
+	$wp_stylesheet_path = null;
+	$wp_template_path   = null;
+
 	/**
 	 * Fires after the theme is switched.
 	 *
diff --git a/tests/phpunit/tests/comment/commentsTemplate.php b/tests/phpunit/tests/comment/commentsTemplate.php
index 7c27bf1d43..cb033a55e3 100644
--- a/tests/phpunit/tests/comment/commentsTemplate.php
+++ b/tests/phpunit/tests/comment/commentsTemplate.php
@@ -9,6 +9,14 @@
  */
 class Tests_Comment_CommentsTemplate extends WP_UnitTestCase {
 
+	/**
+	 * Performs setup tasks for every test.
+	 */
+	public function set_up() {
+		parent::set_up();
+		switch_theme( 'default' );
+	}
+
 	/**
 	 * @ticket 8071
 	 */
diff --git a/tests/phpunit/tests/comment/wpListComments.php b/tests/phpunit/tests/comment/wpListComments.php
index f49ef84561..8997b681f7 100644
--- a/tests/phpunit/tests/comment/wpListComments.php
+++ b/tests/phpunit/tests/comment/wpListComments.php
@@ -6,6 +6,15 @@
  * @covers ::wp_list_comments
  */
 class Tests_Comment_WpListComments extends WP_UnitTestCase {
+
+	/**
+	 * Performs setup tasks for every test.
+	 */
+	public function set_up() {
+		parent::set_up();
+		switch_theme( 'default' );
+	}
+
 	/**
 	 * @ticket 35175
 	 */
diff --git a/tests/phpunit/tests/general/template.php b/tests/phpunit/tests/general/template.php
index 8a29853526..e5b88d7d4d 100644
--- a/tests/phpunit/tests/general/template.php
+++ b/tests/phpunit/tests/general/template.php
@@ -10,6 +10,7 @@
 require_once ABSPATH . 'wp-admin/includes/class-wp-site-icon.php';
 
 class Tests_General_Template extends WP_UnitTestCase {
+
 	protected $wp_site_icon;
 	public $site_icon_id;
 	public $site_icon_url;
@@ -41,6 +42,7 @@ class Tests_General_Template extends WP_UnitTestCase {
 	public function set_up() {
 		parent::set_up();
 
+		switch_theme( 'default' );
 		$this->wp_site_icon = new WP_Site_Icon();
 	}
 
diff --git a/tests/phpunit/tests/template.php b/tests/phpunit/tests/template.php
index 3ae0bf31b8..82505bba8e 100644
--- a/tests/phpunit/tests/template.php
+++ b/tests/phpunit/tests/template.php
@@ -629,6 +629,44 @@ class Tests_Template extends WP_UnitTestCase {
 		);
 	}
 
+	/**
+	 * Tests that `locate_template()` uses the current theme even after switching the theme.
+	 *
+	 * @ticket 18298
+	 *
+	 * @covers ::locate_template
+	 */
+	public function test_locate_template_uses_current_theme() {
+		$themes = wp_get_themes();
+
+		// Look for parent themes with an index.php template.
+		$relevant_themes = array();
+		foreach ( $themes as $theme ) {
+			if ( $theme->get_stylesheet() !== $theme->get_template() ) {
+				continue;
+			}
+			$php_templates = $theme['Template Files'];
+			if ( ! isset( $php_templates['index.php'] ) ) {
+				continue;
+			}
+			$relevant_themes[] = $theme;
+		}
+		if ( count( $relevant_themes ) < 2 ) {
+			$this->markTestSkipped( 'Test requires at least two parent themes with an index.php template.' );
+		}
+
+		$template_names = array( 'index.php' );
+
+		$old_theme = $relevant_themes[0];
+		$new_theme = $relevant_themes[1];
+
+		switch_theme( $old_theme->get_stylesheet() );
+		$this->assertSame( $old_theme->get_stylesheet_directory() . '/index.php', locate_template( $template_names ), 'Incorrect index template found in initial theme.' );
+
+		switch_theme( $new_theme->get_stylesheet() );
+		$this->assertSame( $new_theme->get_stylesheet_directory() . '/index.php', locate_template( $template_names ), 'Incorrect index template found in theme after switch.' );
+	}
+
 	public function assertTemplateHierarchy( $url, array $expected, $message = '' ) {
 		$this->go_to( $url );
 		$hierarchy = $this->get_template_hierarchy();
diff --git a/tests/phpunit/tests/theme.php b/tests/phpunit/tests/theme.php
index 378ed16093..b93edfaf63 100644
--- a/tests/phpunit/tests/theme.php
+++ b/tests/phpunit/tests/theme.php
@@ -36,8 +36,9 @@ class Tests_Theme extends WP_UnitTestCase {
 
 		parent::set_up();
 
+		// Sets up the `wp-content/themes/` directory to ensure consistency when running tests.
 		$this->orig_theme_dir = $wp_theme_directories;
-		$wp_theme_directories = array( WP_CONTENT_DIR . '/themes' );
+		$wp_theme_directories = array( WP_CONTENT_DIR . '/themes', realpath( DIR_TESTDATA . '/themedir1' ) );
 
 		add_filter( 'extra_theme_headers', array( $this, 'theme_data_extra_headers' ) );
 		wp_clean_themes_cache();
@@ -282,6 +283,11 @@ class Tests_Theme extends WP_UnitTestCase {
 
 		for ( $i = 0; $i < 3; $i++ ) {
 			foreach ( $themes as $name => $theme ) {
+				// Skip invalid theme directory names (such as `block_theme-[0.4.0]`).
+				if ( ! preg_match( '/^[a-z0-9-]+$/', $theme['Stylesheet'] ) ) {
+					continue;
+				}
+
 				// Switch to this theme.
 				if ( 2 === $i ) {
 					switch_theme( $theme['Template'], $theme['Stylesheet'] );
@@ -289,16 +295,16 @@ class Tests_Theme extends WP_UnitTestCase {
 					switch_theme( $theme['Stylesheet'] );
 				}
 
-				$this->assertSame( $name, get_current_theme() );
+				$this->assertSame( $theme['Name'], get_current_theme() );
 
 				// Make sure the various get_* functions return the correct values.
 				$this->assertSame( $theme['Template'], get_template() );
 				$this->assertSame( $theme['Stylesheet'], get_stylesheet() );
 
-				$root_fs = get_theme_root();
+				$root_fs = $theme->get_theme_root();
 				$this->assertTrue( is_dir( $root_fs ) );
 
-				$root_uri = get_theme_root_uri();
+				$root_uri = $theme->get_theme_root_uri();
 				$this->assertNotEmpty( $root_uri );
 
 				$this->assertSame( $root_fs . '/' . get_stylesheet(), get_stylesheet_directory() );
@@ -309,19 +315,38 @@ class Tests_Theme extends WP_UnitTestCase {
 				$this->assertSame( $root_fs . '/' . get_template(), get_template_directory() );
 				$this->assertSame( $root_uri . '/' . get_template(), get_template_directory_uri() );
 
-				// get_query_template()
+				// Skip block themes for get_query_template() tests since this test is focused on classic templates.
+				if ( wp_is_block_theme() && current_theme_supports( 'block-templates' ) ) {
+					continue;
+				}
 
 				// Template file that doesn't exist.
 				$this->assertSame( '', get_query_template( 'nonexistant' ) );
 
 				// Template files that do exist.
-				/*
 				foreach ( $theme['Template Files'] as $path ) {
-					$file = basename($path, '.php');
-					FIXME: untestable because get_query_template() uses TEMPLATEPATH.
-					$this->assertSame('', get_query_template($file));
+					$file = basename( $path, '.php' );
+
+					// The functions.php file is not a template.
+					if ( 'functions' === $file ) {
+						continue;
+					}
+
+					// Underscores are not supported by `locate_template()`.
+					if ( 'taxonomy-post_format' === $file ) {
+						$file = 'taxonomy';
+					}
+
+					$child_theme_file  = get_stylesheet_directory() . '/' . $file . '.php';
+					$parent_theme_file = get_template_directory() . '/' . $file . '.php';
+					if ( file_exists( $child_theme_file ) ) {
+						$this->assertSame( $child_theme_file, get_query_template( $file ) );
+					} elseif ( file_exists( $parent_theme_file ) ) {
+						$this->assertSame( $parent_theme_file, get_query_template( $file ) );
+					} else {
+						$this->assertSame( '', get_query_template( $file ) );
+					}
 				}
-				*/
 
 				// These are kind of tautologies but at least exercise the code.
 				$this->assertSame( get_404_template(), get_query_template( '404' ) );
@@ -854,6 +879,184 @@ class Tests_Theme extends WP_UnitTestCase {
 		);
 	}
 
+	/**
+	 * Tests that a theme in the custom test data theme directory is recognized.
+	 *
+	 * @ticket 18298
+	 */
+	public function test_theme_in_custom_theme_dir_is_valid() {
+		switch_theme( 'block-theme' );
+		$this->assertTrue( wp_get_theme()->exists() );
+	}
+
+	/**
+	 * Tests that `is_child_theme()` returns true for child theme.
+	 *
+	 * @ticket 18298
+	 *
+	 * @covers ::is_child_theme
+	 */
+	public function test_is_child_theme_true() {
+		switch_theme( 'block-theme-child' );
+		$this->assertTrue( is_child_theme() );
+	}
+
+	/**
+	 * Tests that `is_child_theme()` returns false for parent theme.
+	 *
+	 * @ticket 18298
+	 *
+	 * @covers ::is_child_theme
+	 */
+	public function test_is_child_theme_false() {
+		switch_theme( 'block-theme' );
+		$this->assertFalse( is_child_theme() );
+	}
+
+	/**
+	 * Tests that the child theme directory is correctly detected.
+	 *
+	 * @ticket 18298
+	 *
+	 * @covers ::get_stylesheet_directory
+	 */
+	public function test_get_stylesheet_directory() {
+		switch_theme( 'block-theme-child' );
+		$this->assertSame( realpath( DIR_TESTDATA ) . '/themedir1/block-theme-child', get_stylesheet_directory() );
+	}
+
+	/**
+	 * Tests that the parent theme directory is correctly detected.
+	 *
+	 * @ticket 18298
+	 *
+	 * @covers ::get_template_directory
+	 */
+	public function test_get_template_directory() {
+		switch_theme( 'block-theme-child' );
+		$this->assertSame( realpath( DIR_TESTDATA ) . '/themedir1/block-theme', get_template_directory() );
+	}
+
+	/**
+	 * Tests that get_stylesheet_directory() behaves correctly with filters.
+	 *
+	 * @ticket 18298
+	 * @dataProvider data_get_stylesheet_directory_with_filter
+	 *
+	 * @covers ::get_stylesheet_directory
+	 *
+	 * @param string   $theme     Theme slug / directory name.
+	 * @param string   $hook_name Filter hook name.
+	 * @param callable $callback  Filter callback.
+	 * @param string   $expected  Expected stylesheet directory with the filter active.
+	 */
+	public function test_get_stylesheet_directory_with_filter( $theme, $hook_name, $callback, $expected ) {
+		switch_theme( $theme );
+
+		// Add filter, then call get_stylesheet_directory() to compute value.
+		add_filter( $hook_name, $callback );
+		$this->assertSame( $expected, get_stylesheet_directory(), 'Stylesheet directory returned incorrect result not considering filters' );
+
+		// Remove filter again, then ensure result is recalculated and not the same as before.
+		remove_filter( $hook_name, $callback );
+		$this->assertNotSame( $expected, get_stylesheet_directory(), 'Stylesheet directory returned previous value even though filters were removed' );
+	}
+
+	/**
+	 * Data provider for `test_get_stylesheet_directory_with_filter()`.
+	 *
+	 * @return array[]
+	 */
+	public function data_get_stylesheet_directory_with_filter() {
+		return array(
+			'with stylesheet_directory filter' => array(
+				'block-theme',
+				'stylesheet_directory',
+				static function ( $dir ) {
+					return str_replace( realpath( DIR_TESTDATA ) . '/themedir1', '/fantasy-dir', $dir );
+				},
+				'/fantasy-dir/block-theme',
+			),
+			'with theme_root filter'           => array(
+				'block-theme',
+				'theme_root',
+				static function () {
+					return '/fantasy-dir';
+				},
+				'/fantasy-dir/block-theme',
+			),
+			'with stylesheet filter'           => array(
+				'block-theme',
+				'stylesheet',
+				static function () {
+					return 'another-theme';
+				},
+				// Because the theme does not exist, `get_theme_root()` returns the default themes directory.
+				WP_CONTENT_DIR . '/themes/another-theme',
+			),
+		);
+	}
+
+	/**
+	 * Tests that get_template_directory() behaves correctly with filters.
+	 *
+	 * @ticket 18298
+	 * @dataProvider data_get_template_directory_with_filter
+	 *
+	 * @covers ::get_template_directory
+	 *
+	 * @param string   $theme     Theme slug / directory name.
+	 * @param string   $hook_name Filter hook name.
+	 * @param callable $callback  Filter callback.
+	 * @param string   $expected  Expected template directory with the filter active.
+	 */
+	public function test_get_template_directory_with_filter( $theme, $hook_name, $callback, $expected ) {
+		switch_theme( $theme );
+
+		// Add filter, then call get_template_directory() to compute value.
+		add_filter( $hook_name, $callback );
+		$this->assertSame( $expected, get_template_directory(), 'Template directory returned incorrect result not considering filters' );
+
+		// Remove filter again, then ensure result is recalculated and not the same as before.
+		remove_filter( $hook_name, $callback );
+		$this->assertNotSame( $expected, get_template_directory(), 'Template directory returned previous value even though filters were removed' );
+	}
+
+	/**
+	 * Data provider for `test_get_template_directory_with_filter()`.
+	 *
+	 * @return array[]
+	 */
+	public function data_get_template_directory_with_filter() {
+		return array(
+			'with template_directory filter' => array(
+				'block-theme',
+				'template_directory',
+				static function ( $dir ) {
+					return str_replace( realpath( DIR_TESTDATA ) . '/themedir1', '/fantasy-dir', $dir );
+				},
+				'/fantasy-dir/block-theme',
+			),
+			'with theme_root filter'         => array(
+				'block-theme',
+				'theme_root',
+				static function () {
+					return '/fantasy-dir';
+				},
+				'/fantasy-dir/block-theme',
+			),
+			'with template filter'           => array(
+				'block-theme',
+				'template',
+				static function () {
+					return 'another-theme';
+				},
+				// Because the theme does not exist, `get_theme_root()` returns the default themes directory.
+				WP_CONTENT_DIR . '/themes/another-theme',
+			),
+		);
+	}
+
 	/**
 	 * Helper function to ensure that a block theme is available and active.
 	 */