[ndesaulniers]

1. Unit tests. Otherwise modifying old code is full of potentially unforeseen landmines.

2. Read the function a few times to get a sense of what it's doing.

3. Break the function into blocks of statements that are performing a related task.

4. Factor those out into smaller functions.

5. Recursively repeat 3-5 until you're satisfied with the new functions' line count.

> Should I tell my manager that the function needs to be refactored and take time to refactor it?

It's absolutely worth mentioning. Time estimations are one of the harder tasks of Software Engineering. Being up front with your manager can help better set expectations.

[rrauenza]

I would add assertions in as well as you iterate. It will validate whether you understand the flow of information through the function.

[phpnode]

Absolutely this. Not only do assertions make it easier to validate your understanding, they capture and preserve that understanding for future developers (including yourself, 6 weeks from now).

Assertions are comments which can always be trusted and which never get out of date. It baffles me that there's so much reluctance to use them (especially in dynamic languages).

[bdavisx]

There's no way to add unit tests to a multi-thousand line method. There's almost no way something that long was written in a testable manner.

You can probably add some tests around the inputs/outputs, depending on the structure. For example you might have to check the database before/after and other things like that. But it won't be "unit" tests in the conventional sense. More like Integration tests, because something that long should not only be multiple methods, but multiple classes.

[afarrell]

Unit tests might be hard on a function like this and you might have to admit that your tests are more integrationey than you'd like.