public function test_post_update_meta_empty_is_allowed_ajax() {
    $p = self::factory()->post->create();

    $m = add_post_meta( $p, 'testkey', 'hello' );

    // Become an administrator.
    $this->_setRole( 'administrator' );

    $_POST = array(
      '_ajax_nonce-add-meta' => wp_create_nonce( 'add-meta' ),
      'post_id'              => $p,
      'meta'                 => array(
        $m => array(
          'key'   => 'testkey',
          'value' => '',
        ),
      ),
    );

    // Make the request.
    try {
      $this->_handleAjax( 'add-meta' );
    } catch ( WPAjaxDieContinueException $e ) {
      unset( $e );
    }

    $this->assertSame( '', get_post_meta( $p, 'testkey', true ) );
  }