test(ai): simplify TestLLM setup

packages/ai/test/exports.test.ts

@@ -32,6 +32,8 @@ describe("public exports", () => {
     expect(Provider.make).toBeFunction()
     expect(ProviderSubpath.make).toBe(Provider.make)
     expect(TestLLM.layer).toBeFunction()
+    expect(TestLLM.layerWithClient).toBeFunction()
+    expect(TestLLM.requests).toBeDefined()
   })
 
   test("route barrel exposes route-authoring APIs", () => {

packages/ai/test/testing.test.ts

@@ -0,0 +1,19 @@
+import { expect } from "bun:test"
+import { Effect } from "effect"
+import { LLM, LLMClient, LLMEvent } from "../src"
+import { OpenAIChat } from "../src/protocols"
+import { TestLLM } from "../src/testing"
+import { testEffect } from "./lib/effect"
+
+const model = OpenAIChat.route.model({ id: "test" })
+const it = testEffect(TestLLM.layerWithClient({ fallback: TestLLM.text("Hello") }))
+
+it.effect("provides a client and exposes received requests", () =>
+  Effect.gen(function* () {
+    const response = yield* LLMClient.generate(LLM.request({ model, prompt: "Say hello" }))
+
+    expect(response.text).toBe("Hello")
+    expect(response.events.filter(LLMEvent.is.textDelta)).toEqual([{ type: "text-delta", id: "text-0", text: "Hello" }])
+    expect(yield* TestLLM.requests).toHaveLength(1)
+  }),
+)