Build/Test Tools: Discard stale roles before reinstalling the test tables

[ekamran]

The test installer loads wp-settings.php before it drops and recreates the test tables, so the global WP_Roles object is created from the previous run's data. populate_roles() then sees the default roles as already existing on that object and writes the stale capabilities back into the fresh tables. Role data from a previous run therefore survives reinstallation until the database is dropped by hand. This affects the Core test installer only, not production WordPress installs.

This change discards the roles object right after the tables are dropped. wp_roles() recreates it lazily inside populate_roles(), which runs after wp_install() has created the fresh tables, so every run starts from the default roles.

Reproduction steps, the full verification list and the same patch as a diff are on the ticket. Verified on single site and multisite install paths, on repeated runs, and end to end on a fresh clone with a new database. WP_TESTS_SKIP_INSTALL=1 behaviour is unchanged.

Trac ticket: https://core.trac.wordpress.org/ticket/65972

Use of AI Tools

AI assistance: Yes
Tool(s): Claude Code, Codex (testing and review)
The investigation, verification and final decisions are mine, and I take responsibility for the change.

[github-actions]

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Props ekamran.

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[github-actions]

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[ekamran]

@lancewillett @desrosj @lucatume — tagging you as Build/Test Tools maintainers.

This one is the test installer writing the previous run's role data back
into freshly created tables. Same failure hosts have hit since 2020
(phpunit-test-runner#110). 9-line patch, repro steps and full verification
on the Trac ticket — single site, multisite, repeated runs and a fresh clone.

https://core.trac.wordpress.org/ticket/65972

[lancewillett]

Ready to land. No review blockers.

I tested with local PHPUnit: 753 single-site and 763 multisite tests passed. Confirmed stale-role failures without the patch and successful cleanup with this change.

[github-actions]

A commit was made that fixes the Trac ticket referenced in the description of this pull request.

SVN changeset: 63590
GitHub commit: f8fb8d0

This PR will be closed, but please confirm the accuracy of this and reopen if there is more work to be done.