function test_wp_make_content_images_responsive() {
    $image_meta = wp_get_attachment_metadata( self::$large_id );
    $size_array = $this->_get_image_size_array_from_meta( $image_meta, 'medium' );

    $srcset = sprintf( 'srcset="%s"', wp_get_attachment_image_srcset( self::$large_id, $size_array, $image_meta ) );
    $sizes  = sprintf( 'sizes="%s"', wp_get_attachment_image_sizes( self::$large_id, $size_array, $image_meta ) );

    // Function used to build HTML for the editor.
    $img                  = get_image_tag( self::$large_id, '', '', '', 'medium' );
    $img_no_size_in_class = str_replace( 'size-', '', $img );
    $img_no_width_height  = str_replace( ' width="' . $size_array[0] . '"', '', $img );
    $img_no_width_height  = str_replace( ' height="' . $size_array[1] . '"', '', $img_no_width_height );
    $img_no_size_id       = str_replace( 'wp-image-', 'id-', $img );
    $img_with_sizes_attr  = str_replace( '<img ', '<img sizes="99vw" ', $img );
    $img_xhtml            = str_replace( ' />', '/>', $img );
    $img_html5            = str_replace( ' />', '>', $img );

    // Manually add srcset and sizes to the markup from get_image_tag();
    $respimg                  = preg_replace( '|<img ([^>]+) />|', '<img $1 ' . $srcset . ' ' . $sizes . ' />', $img );
    $respimg_no_size_in_class = preg_replace( '|<img ([^>]+) />|', '<img $1 ' . $srcset . ' ' . $sizes . ' />', $img_no_size_in_class );
    $respimg_no_width_height  = preg_replace( '|<img ([^>]+) />|', '<img $1 ' . $srcset . ' ' . $sizes . ' />', $img_no_width_height );
    $respimg_with_sizes_attr  = preg_replace( '|<img ([^>]+) />|', '<img $1 ' . $srcset . ' />', $img_with_sizes_attr );
    $respimg_xhtml            = preg_replace( '|<img ([^>]+)/>|', '<img $1 ' . $srcset . ' ' . $sizes . ' />', $img_xhtml );
    $respimg_html5            = preg_replace( '|<img ([^>]+)>|', '<img $1 ' . $srcset . ' ' . $sizes . ' />', $img_html5 );

    $content = '
			<p>Image, standard. Should have srcset and sizes.</p>
			%1$s

			<p>Image, no size class. Should have srcset and sizes.</p>
			%2$s

			<p>Image, no width and height attributes. Should have srcset and sizes (from matching the file name).</p>
			%3$s

			<p>Image, no attachment ID class. Should NOT have srcset and sizes.</p>
			%4$s

			<p>Image, with sizes attribute. Should NOT have two sizes attributes.</p>
			%5$s

			<p>Image, XHTML 1.0 style (no space before the closing slash). Should have srcset and sizes.</p>
			%6$s

			<p>Image, HTML 5.0 style. Should have srcset and sizes.</p>
			%7$s';

    $content_unfiltered = sprintf( $content, $img, $img_no_size_in_class, $img_no_width_height, $img_no_size_id, $img_with_sizes_attr, $img_xhtml, $img_html5 );
    $content_filtered   = sprintf( $content, $respimg, $respimg_no_size_in_class, $respimg_no_width_height, $img_no_size_id, $respimg_with_sizes_attr, $respimg_xhtml, $respimg_html5 );

    $this->assertSame( $content_filtered, wp_make_content_images_responsive( $content_unfiltered ) );
  }