diff --git a/tests/phpunit/tests/theme/customHeader.php b/tests/phpunit/tests/theme/customHeader.php
index 875c8ba79d..98b2c84e02 100644
--- a/tests/phpunit/tests/theme/customHeader.php
+++ b/tests/phpunit/tests/theme/customHeader.php
@@ -6,17 +6,224 @@ class Tests_Theme_Custom_Header extends WP_UnitTestCase {
 
 	static $post;
 
+	protected static $header_video_id;
+
 	public static function wpSetUpBeforeClass( $factory ) {
 		self::$post = self::factory()->post->create( array(
 			'post_status' => 'publish',
 		) );
+
+		$file = DIR_TESTDATA . '/uploads/small-video.mp4';
+		self::$header_video_id = $factory->attachment->create_upload_object( $file );
+	}
+
+	function setUp() {
+		parent::setUp();
+
+		require_once( ABSPATH . WPINC . '/class-wp-customize-manager.php' );
+		$GLOBALS['wp_customize'] = new WP_Customize_Manager();
+		$this->customize_manager = $GLOBALS['wp_customize'];
+
+		wp_dequeue_script( 'wp-custom-header' );
 	}
 
 	function tearDown() {
+		$this->customize_manager = null;
+		unset( $GLOBALS['wp_customize'] );
+
 		remove_theme_support( 'custom-header' );
+		remove_theme_mod( 'header_image' );
+		remove_theme_mod( 'header_image_data' );
+		remove_theme_mod( 'header_video' );
+		remove_theme_mod( 'external_header_video' );
+
 		parent::tearDown();
 	}
 
+	function test_add_and_remove_theme_support() {
+		$this->_add_theme_support();
+		$this->assertTrue( current_theme_supports( 'custom-header' ) );
+		remove_theme_support( 'custom-header' );
+		$this->assertFalse( current_theme_supports( 'custom-header' ) );
+	}
+
+	function test_get_header_image_without_registered_default() {
+		$this->_add_theme_support();
+		$image = get_header_image();
+		$this->assertFalse( has_header_image() );
+		$this->assertEmpty( $image );
+	}
+
+	function test_get_header_image_with_registered_default() {
+		$default = 'http://localhost/default-header.jpg';
+		$this->_add_theme_support( array( 'default-image' => $default ) );
+
+		$image = get_header_image();
+		$this->assertTrue( has_header_image() );
+		$this->assertEquals( $default, $image );
+	}
+
+	function test_get_header_image_from_theme_mod() {
+		$default = 'http://localhost/default-header.jpg';
+		$custom = 'http://localhost/custom-header.jpg';
+		$this->_add_theme_support( array( 'default-image' => $default ) );
+
+		set_theme_mod( 'header_image', $custom );
+		$image = get_header_image();
+		$this->assertEquals( $custom, $image );
+		$this->assertTrue( has_header_image() );
+
+		set_theme_mod( 'header_image', 'remove-header' );
+		$image = get_header_image();
+		$this->assertFalse( has_header_image() );
+		$this->assertFalse( $image );
+	}
+
+	function test_get_header_image_tag_without_registered_default_image() {
+		$this->_add_theme_support();
+		$html = get_header_image_tag();
+		$this->assertEmpty( $html );
+	}
+
+	function test_get_header_image_tag_with_registered_default_image() {
+		$default = 'http://localhost/default-header.jpg';
+		$this->_add_theme_support( array( 'default-image' => $default ) );
+
+		$html = get_header_image_tag();
+		$this->assertStringStartsWith( '<img ', $html );
+		$this->assertContains( sprintf( 'src="%s"', $default ), $html );
+	}
+
+	/**
+	 * @ticket 38633
+	 */
+	function test_get_header_image_tag_with_registered_default_image_and_remove_header_theme_mod() {
+		$default = 'http://localhost/default-header.jpg';
+		$this->_add_theme_support( array( 'default-image' => $default ) );
+
+		set_theme_mod( 'header_image', 'remove-header' );
+		$html = get_header_image_tag();
+		$this->assertEmpty( $html );
+	}
+
+	function test_get_header_image_tag_with_registered_default_image_and_custom_theme_mod() {
+		$default = 'http://localhost/default-header.jpg';
+		$custom = 'http://localhost/custom-header.jpg';
+		$this->_add_theme_support( array( 'default-image' => $default ) );
+
+		set_theme_mod( 'header_image', $custom );
+		$html = get_header_image_tag();
+		$this->assertStringStartsWith( '<img ', $html );
+		$this->assertContains( sprintf( 'src="%s"', $custom ), $html );
+	}
+
+	function test_get_custom_header_markup_without_registered_default_image() {
+		$this->_add_theme_support();
+
+		$html = get_custom_header_markup();
+		$this->assertFalse( has_custom_header() );
+		$this->assertEmpty( $html );
+
+		// The container should always be returned in the Customizer preview.
+		$this->_set_customize_previewing( true );
+		$html = get_custom_header_markup();
+		$this->assertEquals( '<div id="wp-custom-header" class="wp-custom-header"></div>', $html );
+	}
+
+	function test_get_custom_header_markup_with_registered_default_image() {
+		$default = 'http://localhost/default-header.jpg';
+		$this->_add_theme_support( array( 'default-image' => $default ) );
+		$html = get_custom_header_markup();
+		$this->assertTrue( has_custom_header() );
+		$this->assertStringStartsWith( '<div id="wp-custom-header" class="wp-custom-header">', $html );
+		$this->assertContains( sprintf( 'src="%s"', $default ), $html );
+	}
+
+	function test_get_header_video_url() {
+		$this->_add_theme_support( array( 'video' => true ) );
+
+		$this->assertFalse( has_header_video() );
+		set_theme_mod( 'header_video', self::$header_video_id );
+		$this->assertTrue( has_header_video() );
+		$this->assertEquals( wp_get_attachment_url( self::$header_video_id ), get_header_video_url() );
+	}
+
+	function test_get_external_header_video_url() {
+		$external = 'http://example.com/custom-video.mp4';
+		$this->_add_theme_support( array( 'video' => true ) );
+
+		$this->assertFalse( has_header_video() );
+		set_theme_mod( 'external_header_video', $external );
+		$this->assertTrue( has_header_video() );
+		$this->assertEquals( $external, get_header_video_url() );
+	}
+
+	function test_get_header_video_url_prefers_local_video() {
+		$external = 'http://example.com/custom-video.mp4';
+		$this->_add_theme_support( array( 'video' => true ) );
+
+		set_theme_mod( 'header_video', self::$header_video_id );
+		set_theme_mod( 'external_header_video', $external );
+		$this->assertEquals( wp_get_attachment_url( self::$header_video_id ), get_header_video_url() );
+	}
+
+	function test_get_custom_header_markup_with_video_and_without_an_image() {
+		$custom = 'http://localhost/custom-video.mp4';
+		$this->_add_theme_support( array( 'video' => true, 'video-active-callback' => '__return_true' ) );
+
+		set_theme_mod( 'external_header_video', $custom );
+		$html = get_custom_header_markup();
+		$this->assertTrue( has_header_video() );
+		$this->assertTrue( has_custom_header() );
+		$this->assertEquals( '<div id="wp-custom-header" class="wp-custom-header"></div>', $html );
+	}
+
+	function test_header_script_is_not_enqueued_by_the_custom_header_markup_without_video() {
+		$this->_add_theme_support( array( 'video' => true, 'video-active-callback' => '__return_true' ) );
+
+		ob_start();
+		the_custom_header_markup();
+		ob_end_clean();
+		$this->assertFalse( wp_script_is( 'wp-custom-header', 'enqueued' ) );
+
+		set_theme_mod( 'header_image', 'http://localhost/custom-header.jpg' );
+
+		ob_start();
+		the_custom_header_markup();
+		ob_end_clean();
+		$this->assertFalse( wp_script_is( 'wp-custom-header', 'enqueued' ) );
+	}
+
+	function test_header_script_is_not_enqueued_by_the_custom_header_markup_when_active_callback_is_false() {
+		$this->_add_theme_support( array( 'video' => true, 'video-active-callback' => '__return_false' ) );
+		set_theme_mod( 'external_header_video', 'http://localhost/custom-video.mp4' );
+
+		ob_start();
+		the_custom_header_markup();
+		ob_end_clean();
+		$this->assertFalse( wp_script_is( 'wp-custom-header', 'enqueued' ) );
+	}
+
+	function test_header_script_is_enqueued_by_the_custom_header_markup_without_video_when_previewing_in_customizer() {
+		$this->_add_theme_support( array( 'video' => true, 'video-active-callback' => '__return_true' ) );
+		$this->_set_customize_previewing( true );
+
+		ob_start();
+		the_custom_header_markup();
+		ob_end_clean();
+		$this->assertTrue( wp_script_is( 'wp-custom-header', 'enqueued' ) );
+	}
+
+	function test_header_script_is_enqueued_by_the_custom_header_markup_with_video() {
+		$this->_add_theme_support( array( 'video' => true, 'video-active-callback' => '__return_true' ) );
+		set_theme_mod( 'external_header_video', 'http://localhost/custom-video.mp4' );
+
+		ob_start();
+		the_custom_header_markup();
+		ob_end_clean();
+		$this->assertTrue( wp_script_is( 'wp-custom-header', 'enqueued' ) );
+	}
+
 	/**
 	 * @ticket 38738
 	 */
@@ -122,4 +329,11 @@ class Tests_Theme_Custom_Header extends WP_UnitTestCase {
 			'video-active-callback' => 'is_front_page',
 		) );
 	}
+
+	function _set_customize_previewing( $value ) {
+		$class = new ReflectionClass( 'WP_Customize_Manager' );
+		$property = $class->getProperty( 'previewing' );
+		$property->setAccessible( true );
+		$property->setValue( $this->customize_manager, $value );
+	}
 }