To Test or Not to Test?

OK, I'll stop with the silly Shakespearean silliness.

Why do we test everything?

I'm talking about one line of code like this:

Before

WHERE line_of_business IN ( 'XYZ', 'ABC' )

After

WHERE line_of_business IN ( 'XYZ', 'ABC', '123' )

(this was the cause of my first screwup)

I added an extra filter on the IN list. Does that really require the complete testing of the entire (say 8 hour) process?

I've been in IT for 5+ years now and I understand the importance of testing, but this seems a tad ridiculous to me.

Is there a better way? Unit testing performed by another developer? Visual inspection by the DBA or group of peers?