Fix add method in test suite object-cache.php

[spacedmonkey]

In the bundled object-cache.php the add method does not work as expected. The add method, does not check to see if key existing before setting it. Other object caches in the space do this check.

• ​Example 1.
• ​Example 2.
• ​Example 3.

Trac ticket: https://core.trac.wordpress.org/ticket/57963#ticket

[spacedmonkey]

In 55577:

Build/Test Tools: Fix issue with add method in object-cache.php.

In the object-cache.php file used for unit tests, the add method did not work as expected. Other object cache plugins and core, have a check to see if the key exists in memory before writing it. Without this check, it used to write unnecessarily to the cache.

Props spacedmonkey, SergeyBiryukov.
Fixes #57963.

[SergeyBiryukov]

In 55581:

Tests: Consistently sanitize expiration in the test suite's Memcached implementation.

In a previous commit, the ::sanitize_expiration() call in the ::add() method was moved closer to where the value is used.

This commit does the same for the other methods:

• ::cas()
• ::replace()
• ::set()
• ::setMulti()

Follow-up to [40561], [55577].

See #57841, #57963.

Committed at https://core.trac.wordpress.org/changeset/55577