New instance per request or per test worker? (Vitest)

[0xOlias]

I'm planning to adopt anvil.js with Vitest, but it's not clear to me how new Anvil instances are spawned when using startProxy. Is it truly per request as the docs suggest, or is it per vitest test worker?

Seems like there are several possible ways that this might behave:

1. Fresh instance per (RPC) request
2. Fresh instance per test
3. Fresh instance per test worker

I also imagine this depends on the Vitest threads config. Appreciate any additional info - thanks for building this!

[fubhy]

It's per id. And since you'd use one id per test thread, it's per test essentially.

With this, you can completely drop the threads option (default is true) and simply let vitest decide how many cores to utilize for your test runs in parallel.

Check out the example here:

This sets up globalSetup.ts (see vitest.config.ts). It starts a global proxy for the entire test suite:
https://github.com/wagmi-dev/anvil.js/blob/b09bd0ec8013a674dcc5dbe6885e12425bd1f823/examples/example-vitest/tests/globalSetup.ts#L1-L14

Then, you would configure your rpc clients (e.g. with viem) to use http / ws rpc urls like this: http://127.0.0.1:8545/1. Note the /1 suffix. In a vitest setup, you'd not hard-code that to /1 but to /${process.env.VITEST_POOL_ID}. Hence: http://127.0.0.1:8545/${process.env.VITEST_POOL_ID. E.g see here:

https://github.com/wagmi-dev/anvil.js/blob/b09bd0ec8013a674dcc5dbe6885e12425bd1f823/examples/example-vitest/tests/utils.ts#L9-L24

And then, you can optionally reset your anvil instance after each test file (or whatever suits your setup):

https://github.com/wagmi-dev/anvil.js/blob/b09bd0ec8013a674dcc5dbe6885e12425bd1f823/examples/example-vitest/tests/setup.ts#L6-L12

You can also print the anvil logs if a test failed:

https://github.com/wagmi-dev/anvil.js/blob/b09bd0ec8013a674dcc5dbe6885e12425bd1f823/examples/example-vitest/tests/setup.ts#L14-L21

[fubhy]

We should probably link directly to this example from the readme!

[fubhy]

I fixed the wording in the readme file.

[fubhy]

Viem already has this setup integrated btw. Logs are printed here for instance: https://github.com/wagmi-dev/viem/actions/runs/4810645056/jobs/8563603002#step:4:926

[fubhy]

https://github.com/wagmi-dev/viem/blob/main/src/_test/setup.ts#L40-L59

[0xOlias]

Thanks, this is very helpful. Just noticed an added benefit of using anvil.js - no longer need to remember to run anvil before running pnpm test 😁