public function test_doing_filter_real() {
    $this->assertFalse( doing_filter() );            // No filter is passed in, and no filter is being processed.
    $this->assertFalse( doing_filter( 'testing' ) ); // Filter is passed in but not being processed.

    add_filter( 'testing', array( $this, 'apply_testing_filter' ) );
    $this->assertTrue( has_action( 'testing' ) );
    $this->assertSame( 10, has_action( 'testing', array( $this, 'apply_testing_filter' ) ) );

    apply_filters( 'testing', '' );

    // Make sure it ran.
    $this->assertTrue( $this->apply_testing_filter );

    $this->assertFalse( doing_filter() );            // No longer doing any filters.
    $this->assertFalse( doing_filter( 'testing' ) ); // No longer doing this filter.
  }