Throw error when `getTestDatabase()` is called inside `beforeTemplateIsBaked()` instead of hanging

[codetheweb]

Also should document this behavior in the README and add a test.

[itelo]

@codetheweb I have no idea how to do that, I tried to search for solutions, but all of them seem flaky. Do you have any suggestions? I believe a good decision is to have good documentation about this

[codetheweb]

Sure, some debug logging might be helpful in tracking down the issue but I believe it hangs somewhere in this function:

ava-postgres/src/worker.ts

Line 42 in 805474d

public async handleMessage(

I think (if I remember correctly) it's hanging because:

1. the worker sends the test process a request to run the beforeTemplateIsBaked() hook
2. the test process begins running the hook
3. as part of the hook, the test process makes a new GET_TEST_DATABASE request to the worker
4. the worker ignores the message because it's not the expected response (the result of the beforeTemplateIsBaked() hook) and everything hangs

So we just need to add detection of the GET_TEST_DATABASE message type to the worker when in the context of waiting for the result of beforeTemplateIsBaked() and throw.