Cache: Invalid usage of `! $count`

[r-a-y]

In some of our object cache calls (see r2618), we do this:

if ( ! $count = wp_cache_get( 'WHATEVER', 'bp' ) {
	$count = FUNCTION_TO_FETCH_COUNT_VIA_DB();
	wp_cache_set( 'WHATEVER', $count, 'bp' );
}

If $count is zero, then the check passes due to the liberal ! condition and will go about hitting the DB again.

Attached patch fixes this.

[boonebgorges]

Unit tests would be swell (maybe count $wpdb->num_queries before and after count requests that return 0) but this looks like a good change. +1

[DJPaul]

Yes looks fine, and is the way it should have been done originally. I am less concerned about unit tests for this than Boone probably is; either way, let's get the fix in. :)

[DJPaul]

Boone: do you want unit tests before we change these? I was about to commit it as we've been "doing it wrong".

[r-a-y]

I've added unit tests for groups and blogs in unit-tests.patch.

Unit tests fail without 01.patch and pass with 01.patch applied.

Note: I didn't add a test for members because there is always a member created during unit tests.

[boonebgorges]

6012.unit-tests.2.patch​ adds a test for the members function. Since the main purpose of the test is to check whether we're respecting the cached value, we can just force that value, even if it's not accurate. Could also do the same for the other tests, but it doesn't matter too much (those tests effectively just cast a slightly broader net). Feel free to change the group names to be consistent.

[johnjamesjacoby]

Patches look good. Agree with Paul that tests here aren't blockers.

[boonebgorges]

Agree with Paul that tests here aren't blockers.

:weeping_in_corner:

[r-a-y]

In 9231:

Check cache for count functions that return zero.

Some of our count functions were previously setting counts of zero
correctly, but the functions themselves were not referencing the cache
properly when the count returned zero. This led to unnecessary database
queries and we hate extra queries!

This commit addresses the problem and adds unit tests.

Props r-a-y, boonebgorges.

Fixes #6012.