T-SQL Parse Int without fear of exception

Utils.TryParseInt64.sql

-- =============================================
-- Author: Josh Einstein
-- Create date: 2012-06-27
-- Description: Converts a string to Int64 and returns null if the conversion fails.
-- I have tried pretty hard to ensure this can never cause an error. Let me know if
-- I have missed something!
-- =============================================
CREATE FUNCTION [Utils].[TryParseInt64] (@Value nvarchar(255)) RETURNS bigint AS
BEGIN

	IF @Value IS NULL RETURN NULL;

	SET @Value = LTRIM(RTRIM(@Value))

	-- Basic checks for way too long strings or empty strings
	IF LEN(@Value) = 0 OR LEN(@Value) > 38 RETURN NULL;

	-- Since ISNUMERIC returns true for exponent and decimal
	-- number formats, we will tack on a string that won't change
	-- the actual value but will make such strings malformed.
	-- example, if '1.5e15' is the string we'll check '1.5e15.0e0'
	-- which ISNUMERIC won't report as numeric.
	IF ISNUMERIC(@Value + '.0e0') = 0 RETURN NULL;

	-- Use numeric(38,0) because
	-- a) it's the most number of digits we can parse using built-in types
	-- b) we already verified the string contains no decimals
	-- Once we have a numeric type, we can do range checks for int type
	DECLARE @Result numeric(38,0) = CONVERT(numeric(38,0), @Value);
	IF @Result > 9223372036854775807 OR @Result < -9223372036854775808 RETURN NULL;

	RETURN CONVERT(bigint, @Result);

END

Utils.TryParseInt64.Test.sql

-- these should not parse because of the string format
IF Utils.TryParseInt64(NULL) IS NOT NULL RAISERROR('Fail', 16, 1);
IF Utils.TryParseInt64('') IS NOT NULL RAISERROR('Fail', 16, 1);
IF Utils.TryParseInt64(' ') IS NOT NULL RAISERROR('Fail', 16, 1);
IF Utils.TryParseInt64('  ') IS NOT NULL RAISERROR('Fail', 16, 1);
IF Utils.TryParseInt64('.') IS NOT NULL RAISERROR('Fail', 16, 1);
IF Utils.TryParseInt64('0.0') IS NOT NULL RAISERROR('Fail', 16, 1);
IF Utils.TryParseInt64('0.') IS NOT NULL RAISERROR('Fail', 16, 1);
IF Utils.TryParseInt64('.0') IS NOT NULL RAISERROR('Fail', 16, 1);
IF Utils.TryParseInt64('1,000') IS NOT NULL RAISERROR('Fail', 16, 1);
IF Utils.TryParseInt64('$1000') IS NOT NULL RAISERROR('Fail', 16, 1);
IF Utils.TryParseInt64('1.0e0') IS NOT NULL RAISERROR('Fail', 16, 1);
IF Utils.TryParseInt64('0 1') IS NOT NULL RAISERROR('Fail', 16, 1);

-- these should not parse because they overflow
IF Utils.TryParseInt64('9999999999999999999') IS NOT NULL RAISERROR('Fail', 16, 1);	-- # of digits ok, but too large
IF Utils.TryParseInt64('-9999999999999999999') IS NOT NULL RAISERROR('Fail', 16, 1); -- # of digits ok, but too small
IF Utils.TryParseInt64('9223372036854775808') IS NOT NULL RAISERROR('Fail', 16, 1); -- # of digits ok, max + 1
IF Utils.TryParseInt64('-9223372036854775809') IS NOT NULL RAISERROR('Fail', 16, 1); -- # of digits ok, min - 1
IF Utils.TryParseInt64('99999999999999999999') IS NOT NULL RAISERROR('Fail', 16, 1);	-- one too many digits
IF Utils.TryParseInt64('-99999999999999999999') IS NOT NULL RAISERROR('Fail', 16, 1); -- one too many digits
IF Utils.TryParseInt64('99999999999999999999999999999999999999') IS NOT NULL RAISERROR('Fail', 16, 1);	-- max digits for numeric(38)
IF Utils.TryParseInt64('-99999999999999999999999999999999999999') IS NOT NULL RAISERROR('Fail', 16, 1); -- max digits for numeric(38)
IF Utils.TryParseInt64('99999999999999999999999999999999999999999999999999') IS NOT NULL RAISERROR('Fail', 16, 1);	-- way too many digits (50)
IF Utils.TryParseInt64('-99999999999999999999999999999999999999999999999999') IS NOT NULL RAISERROR('Fail', 16, 1); -- way too many digits (50)

-- these should parse fine!
IF NOT (Utils.TryParseInt64('0') = 0) RAISERROR('Fail', 16, 1);
IF NOT (Utils.TryParseInt64('-0') = 0) RAISERROR('Fail', 16, 1);
IF NOT (Utils.TryParseInt64('1') = 1) RAISERROR('Fail', 16, 1);
IF NOT (Utils.TryParseInt64(' 1') = 1) RAISERROR('Fail', 16, 1);
IF NOT (Utils.TryParseInt64('1 ') = 1) RAISERROR('Fail', 16, 1);
IF NOT (Utils.TryParseInt64(' 1 ') = 1) RAISERROR('Fail', 16, 1);
IF NOT (Utils.TryParseInt64('0001') = 1) RAISERROR('Fail', 16, 1);
IF NOT (Utils.TryParseInt64('-1') = -1) RAISERROR('Fail', 16, 1);
IF NOT (Utils.TryParseInt64(' -1') = -1) RAISERROR('Fail', 16, 1);
IF NOT (Utils.TryParseInt64('-1 ') = -1) RAISERROR('Fail', 16, 1);
IF NOT (Utils.TryParseInt64(' -1 ') = -1) RAISERROR('Fail', 16, 1);
IF NOT (Utils.TryParseInt64('-0001') = -1) RAISERROR('Fail', 16, 1);
IF NOT (Utils.TryParseInt64('9223372036854775807') = 9223372036854775807) RAISERROR('Fail', 16, 1);	-- max
IF NOT (Utils.TryParseInt64('-9223372036854775808') = -9223372036854775808) RAISERROR('Fail', 16, 1);	-- min