Query To Get Column Name With Specific Value

Here is tested schema

if exists (select * from dbo.sysobjects where id =
object_id(N'[dbo].[TestTable]') and OBJECTPROPERTY(id, N'IsUserTable')
= 1)
drop table [dbo].[TestTable]
GO

CREATE TABLE [dbo].[TestTable] (
[SerialNumber] [char] (12) COLLATE SQL_Latin1_General_CP1_CI_AS NULL
,
[test1] [char] (4) COLLATE SQL_Latin1_General_CP1_CI_AS NULL ,
[test2] [char] (4) COLLATE SQL_Latin1_General_CP1_CI_AS NULL ,
[test3] [char] (4) COLLATE SQL_Latin1_General_CP1_CI_AS NULL ,
[test4] [char] (4) COLLATE SQL_Latin1_General_CP1_CI_AS NULL
) ON [PRIMARY]
GO

insert into testtable values ('123','pass',null,'fail','skip')
insert into testtable values ('456','fail',null,'pass','skip')
insert into testtable values ('789',null,'fail','skip','pass')
insert into testtable values ('345','pass','pass','pass','fail')



I would like to fetch the COLUMNNAME where the value is fail.
Basically I need to know which test failed, test1, test2, test3 or
test4?

Is this possible?