SQL Server ##error not working. Doesn't go into "if" - sql

Question

I wrote a very simple procedure. I am deliberately making a mistake in the procedure. but the error is not working. I want to return the error I want with raiserror. but it doesn't even go inside the "if".
ALTER PROCEDURE dene
AS
BEGIN
SET NOCOUNT ON;
INSERT INTO bddksektor ([tcmbkodu], [aktif], [bddksektorkodu])
VALUES ('a', 1, 1)
-- I knowingly made a mistake. normally the 1st parameter is int.
-- I'm entering varchar so that it can enter "if" and return an error. but it doesn't
IF ##ERROR <> 0
BEGIN
RAISERROR('Hata', 16, 1, 61106)
RETURN 61106
END
ELSE
BEGIN
SELECT
[tcmbkodu], [aktif], [bddksektorkodu]
FROM
[dbfactoringtest].[dbo].[bddksektor]
ORDER BY
tcmbkodu ASC
END
SET NOCOUNT OFF
END
SQL Server returns its own error when I run the procedure. It does not return the error I wrote because it does not enter the "if"
Error:
Msg 245, Level 16, State 1, Procedure dene, Line 11 [Batch Start Line 1]
Conversion failed when converting the varchar value 'a' to data type int

Answer 1

As I mention in the comment, use a TRY...CATCH. For your SQL if the first INSERT fails the batch will be aborted, and so the IF won't be entered, because it won't be reached. I also recommend switching to THROW instead of RAISERROR as noted in the documentation:
Note
The RAISERROR statement does not honor SET XACT_ABORT. New applications should use THROW instead of RAISERROR.
This gives you something like this:
CREATE OR ALTER PROCEDURE dbo.dene AS --Always schema qualify
BEGIN
SET NOCOUNT ON;
SET XACT_ABORT ON;
BEGIN TRY
INSERT INTO dbo.bddksektor ([tcmbkodu],[aktif],[bddksektorkodu]) --Always schema qualify
VALUES ('a',1,1);
SELECT [tcmbkodu]
,[aktif]
,[bddksektorkodu]
FROM [dbfactoringtest].[dbo].[bddksektor] --Why is this using 3 part naming? Is this copy of bddksektor in a different database?
ORDER BY tcmbkodu ASC;
END TRY
BEGIN CATCH
THROW 61106, N'Hata', 16;
RETURN 61106;
END CATCH;
SET NOCOUNT OFF;
END