[vitest-pool-workers] Add option to disable automatic main entrypoint import

[MonsterDeveloper]

Describe the solution

Currently, when the main option is specified in WorkersPoolOptions, the plugin automatically imports and loads the worker entrypoint. Even when main is set to null or undefined, the plugin falls back to reading from the wrangler config file. For users who only run unit tests and don't need integration testing capabilities, this automatic import requires extensive mocking setup that isn't necessary for their use case.

Describe the solution you'd like
Add a new option to WorkersPoolOptions that allows disabling the automatic import of the main entrypoint:

interface WorkersPoolOptions {
  main?: string;
  autoImportMain?: boolean; // New option, defaults to true for backward compatibility
  // ... other existing options
}

When autoImportMain is set to false, the plugin would:

• Not automatically import the worker entrypoint (regardless of main option or wrangler config)
• Disable integration testing tests with SELF import
• Skip the fallback to wrangler config's main field
• Allow pure unit testing without worker entrypoint overhead

Describe alternatives you've considered

• Currently using a no-op worker as a workaround:

  export default {
    fetch: () => new Response("Not implemented", { status: 500 }),
  }

• Extensive mocking setup (but this adds unnecessary complexity for unit-only tests)

Additional context
This would be particularly beneficial for developers who:

• Only write unit tests for individual functions/modules
• Don't need integration testing with SELF
• Want to avoid the complexity of mocking worker runtime dependencies
• Prefer a lightweight test setup focused purely on unit testing

Use case
Unit-only testing scenarios where integration testing capabilities are not needed, and the automatic entrypoint import creates unnecessary setup overhead and complexity.

[penalosa]

This seems like a great feature (and I've added it to our backlog). Out of interest though, if you're not using the integration testing features (SELF.fetch()), what issues is the main auto-import causing?

[MonsterDeveloper]

Thank you @penalosa

In my worker, since I'm using import { env } from "cloudflare:workers", when the entrypoint is imported and the environment doesn't have correct vars, it throws a bunch of errors.

The point is I don't need to test my whole worker just yet. I'm writing unit tests incrementally and this import just forces my to do extra setup for integration tests I don't even need.

It would actually be cool to detect whether the tests are using SELF to conditionally import the entrypoint just when it's needed.