public function test_remove_filter() {
    $a   = new MockAction();
    $tag = __FUNCTION__;
    $val = __FUNCTION__ . '_val';

    add_filter( $tag, array( $a, 'filter' ) );
    $this->assertSame( $val, apply_filters( $tag, $val ) );

    // Make sure our hook was called correctly.
    $this->assertSame( 1, $a->get_call_count() );
    $this->assertSame( array( $tag ), $a->get_tags() );

    // Now remove the filter, do it again, and make sure it's not called this time.
    remove_filter( $tag, array( $a, 'filter' ) );
    $this->assertSame( $val, apply_filters( $tag, $val ) );
    $this->assertSame( 1, $a->get_call_count() );
    $this->assertSame( array( $tag ), $a->get_tags() );

  }