Re: Freezing localtimestamp and other time function on some value

On Tue, Apr 12, 2016 at 8:37 AM, Alex Ignatov <a.ignatov@postgrespro.ru> wrote:

On 12.04.2016 18:01, Adrian Klaver wrote:

>>I do it by having the date be one of the function arguments and have the default be something like current_date. When I test I supply a date to override the default. This allows for testing the various scenarios by changing the supplied date.

With that approach you have to say application programmer - 'Hey dude, please edit this piece of code for my purpose and after that rollback it'.  I think that it is unacceptable in large project...

​ CREATE FUNCTION do_some_date_based_stuff(reference_date date, other_args) [...]

CREATE FUNCTION production_wrapper_for_above(other_args) [...]

AS $$

SELECT do_some_date_based_stuff(now(), other_args);

$$ ​;

Easy to test do_some_date_based_stuff since it has fewer if any external dependencies.  Shouldn't need to test the wrapper that simply calls the "do_some..." with a default value of the current date.

You might be able to define an appropriate function signature that avoids having to write the wrapper though regardless there is no need to have a different environment for testing versus production if approached in this manner.  You just need to decide on the most desirable way to make it work.

David J.

I know that we can always write some wrappers etc, etc.
This approach would failed if your do_some_date_based_stuff have no date args and contains calls say to now()(or other time function what possible can have fix value ) inside it.

Also wrappers lead to  multiple code base,yours client side code needs to know what function  we should use - test or production. Also with your approach  application server needs to know its working mode test / prod

You always should keep in mind that your application may run in test mode (future/past time) and maintain this code. While with my proposal you  can always use some time function(now or localtimestamp or whatever)  which you can  freeze at anytime on DB level, not operation system(using some 3rd libs) or application(using wrappers and other hacks).

-- 
Alex Ignatov
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company