test(coderd/database): share one database across TestGetUserStatusCounts subtests - #29464

TestGetUserStatusCounts cloned a Postgres database for each of its 756 leaf subtests (6 timezones x 7 report dates x 18 scenarios). The leaves only need query isolation, so they now run inside a rolled-back transaction on one shared database via a new dbtestutil.StartRolledBackTx helper (the rollback counterpart of the existing StartTx). Fixtures, assertions, subtest names and parallelism are unchanged.

One database per scenario, as first sketched, does not work here: every fixture derives from the case's reportUntil and the query aggregates over all users, so users from different dates cannot coexist in one database without changing every expected count. Per-transaction isolation keeps the fixtures byte-identical. The two deleted-user scenarios set deleted_at through the Store (UpdateUserStatus with the intended updated_at, which the deletion trigger copies into user_deleted) instead of raw SQL, because a transaction-bound Store cannot run raw statements; the resulting user_status_changes and user_deleted rows are the same as before.

Before / After

Local, go test -count=1 -tags=testsmallbatch -parallel=8:

The remaining 28s is the query itself being JIT-compiled per call, which #29465 removes; the two changes compose.

Validation

• go test -count=1 -tags=testsmallbatch -parallel=8 ./coderd/database/ -run '^TestGetUserStatusCounts$' -v passes with 925 subtests
• go test -count=2 -shuffle=on -race -run '^TestGetUserStatusCounts$' ./coderd/database/ passes (shared-fixture leakage check)
• golangci-lint run on coderd/database/ and coderd/database/dbtestutil/: 0 issues
• Repository pre-commit hook passed on the commit

Part of the test-suite speedup series (see #29457).

Remote validation

Remote run on a dogfood workspace (separate compute), chat https://dogfood.cdr.dev/agents/5bbe73d0-866a-4841-9cc3-c5e5b4d97e44, tested head 16c8d556c4d against base 9d973372774 on the same machine: ./coderd/database/ -run '^TestGetUserStatusCounts$' 46.97s to 15.05s (925 subtests, 925 pass on both); ./coderd/database/ 56.43s to 22.66s; -race -count=2 -shuffle=on on the test: pass; -parallel=1: ok 23.3s (the rolled-back transactions do not deadlock when serialized). With #29465 cherry-picked on top: test ok 0.58s, package ok 7.49s. Endorsed verdict: PASS.

Xum (an AI agent) authored this PR on behalf of @ibetitsmike.