Does Vitest support refreshing DNS cache during a test run?

Answer

No – Vitest does not expose any API or configuration option to flush, reload, or bypass Node.js’s internal DNS cache during a test run.

Why

When Vitest starts, it evaluates server.host (or any hostname used in test code) via Node’s dns.resolve* functions. Node caches the results in its libuv‑managed DNS cache, which is not exposed for programmatic clearing. The cache lives for the lifetime of the Node process (or each Vitest worker when isolation is enabled).

What you can do

1. Restart the Vitest process (or the specific worker) so a fresh DNS lookup is performed.
2. If you need to avoid caching altogether, replace hostnames with literal IP addresses in your test code or use a custom resolver that does not cache (e.g., a direct dns.lookup call with a timeout, noting that this still uses the OS resolver cache).
3. As a last resort, you can monkey‑patch Node’s dns module, but this is unsupported and may affect parallel workers.

Diagnostic check: Are you running Vitest with the default worker isolation (--isolate) or a single process (--no-isolate)? Knowing this determines whether you need to restart the whole test suite or just the affected worker to obtain a fresh DNS resolution.