Actor isolation in unit tests

README.md

Actor isolation in unit tests

Automated tests with actors can result in using await across many lines which is a lot of lock/unlock cycles which can have some unwanted side effects. In the very least it can just make your unit tests run more slowly. I wanted to see how I could set up my tests to evaluation expectations within the isolated actor scope. I found I could use an isolated parameter with a block to do it. See the code snippet for the function below.

private func run(_ actorInstance: <#actor type#>,
                 block: @Sendable (isolated <#actor type#>) async -> Void) async {
    await block(actorInstance)
}

Then in a test it is not necessary to include multiple await statements to enter the isolated context repeatedly.

await run(state) { state in
    #expect(state.count == 1)
    #expect(state.names.contains("Funches")
}

This works by running the block in the isolated context of the actor due to the isolated parameter of the block.