diff --git a/packages/effect-fc/test/Query.test.ts b/packages/effect-fc/test/Query.test.ts
new file mode 100644
index 0000000..ee6544f
--- /dev/null
+++ b/packages/effect-fc/test/Query.test.ts
@@ -0,0 +1,169 @@
+import { Effect, Option, type Scope, Stream } from "effect"
+import { describe, expect, it } from "vitest"
+import * as Query from "../src/Query.js"
+import * as QueryClient from "../src/QueryClient.js"
+import * as Result from "../src/Result.js"
+
+
+const runQueryTest = <A, E>(effect: Effect.Effect<A, E, QueryClient.QueryClient | Scope.Scope>) =>
+    Effect.runPromise(Effect.scoped(effect.pipe(
+        Effect.provide(QueryClient.QueryClient.Default),
+    )))
+
+const expectSuccessValue = <A, E, P>(
+    result: Result.Result<A, E, P>,
+): A => {
+    expect(Result.isSuccess(result)).toBe(true)
+
+    if (!Result.isSuccess(result))
+        throw new Error(`Expected Success result, received ${result._tag}`)
+
+    return result.value
+}
+
+const expectSomeValue = <A>(option: Option.Option<A>): A => {
+    expect(Option.isSome(option)).toBe(true)
+
+    if (!Option.isSome(option))
+        throw new Error("Expected Some option, received None")
+
+    return option.value
+}
+
+describe("Query", () => {
+    it("fetch caches successful results until they are invalidated or stale", async () => {
+        let calls = 0
+        const key = Stream.empty as Stream.Stream<readonly [number]>
+
+        const result = await runQueryTest(Effect.gen(function*() {
+            const query = yield* Query.make({
+                key,
+                f: ([id]: readonly [number]) => Effect.sync(() => {
+                    calls += 1
+                    return `value:${id}:${calls}`
+                }),
+                staleTime: "1 minute",
+            })
+
+            const first = yield* query.fetch([1])
+            const second = yield* query.fetch([1])
+
+            return [first, second] as const
+        }))
+
+        expect(calls).toBe(1)
+        expect(result[0]._tag).toBe("Success")
+        expect(result[1]._tag).toBe("Success")
+        expect(expectSuccessValue(result[0])).toBe("value:1:1")
+        expect(expectSuccessValue(result[1])).toBe("value:1:1")
+    })
+
+    it("refresh reruns the latest query key", async () => {
+        let calls = 0
+        const key = Stream.empty as Stream.Stream<readonly [number]>
+
+        const result = await runQueryTest(Effect.gen(function*() {
+            const query = yield* Query.make({
+                key,
+                f: ([id]: readonly [number]) => Effect.sync(() => {
+                    calls += 1
+                    return `value:${id}:${calls}`
+                }),
+                staleTime: "0 millis",
+            })
+
+            const first = yield* query.fetch([1])
+            yield* Effect.sleep("1 millis")
+            const refreshed = yield* query.refresh
+
+            return [first, refreshed] as const
+        }))
+
+        expect(calls).toBe(2)
+        expect(expectSuccessValue(result[0])).toBe("value:1:1")
+        expect(expectSuccessValue(result[1])).toBe("value:1:2")
+    })
+
+    it("invalidateCacheEntry forces the next fetch for that key to rerun", async () => {
+        let calls = 0
+        const key = Stream.empty as Stream.Stream<readonly [number]>
+
+        const result = await runQueryTest(Effect.gen(function*() {
+            const query = yield* Query.make({
+                key,
+                f: ([id]: readonly [number]) => Effect.sync(() => {
+                    calls += 1
+                    return `value:${id}:${calls}`
+                }),
+                staleTime: "1 minute",
+            })
+
+            const first = yield* query.fetch([1])
+            yield* query.invalidateCacheEntry([1])
+            const second = yield* query.fetch([1])
+
+            return [first, second] as const
+        }))
+
+        expect(calls).toBe(2)
+        expect(expectSuccessValue(result[0])).toBe("value:1:1")
+        expect(expectSuccessValue(result[1])).toBe("value:1:2")
+    })
+
+    it("invalidateCache clears cached entries for the query function", async () => {
+        let calls = 0
+        const key = Stream.empty as Stream.Stream<readonly [number]>
+
+        const result = await runQueryTest(Effect.gen(function*() {
+            const query = yield* Query.make({
+                key,
+                f: ([id]: readonly [number]) => Effect.sync(() => {
+                    calls += 1
+                    return `value:${id}:${calls}`
+                }),
+                staleTime: "1 minute",
+            })
+
+            const first = yield* query.fetch([1])
+            yield* query.invalidateCache
+            const second = yield* query.fetch([1])
+
+            return [first, second] as const
+        }))
+
+        expect(calls).toBe(2)
+        expect(expectSuccessValue(result[0])).toBe("value:1:1")
+        expect(expectSuccessValue(result[1])).toBe("value:1:2")
+    })
+
+    it("service starts the key stream automatically and updates latest state", async () => {
+        let calls = 0
+        const key = Stream.make([1] as const) as Stream.Stream<readonly [number]>
+
+        const effect = Effect.gen(function*() {
+            const query = yield* Query.service({
+                key,
+                f: ([id]: readonly [number]) => Effect.sync(() => {
+                    calls += 1
+                    return `value:${id}:${calls}`
+                }),
+                staleTime: "1 minute",
+            })
+
+            yield* Effect.sleep("10 millis")
+
+            return {
+                final: yield* query.result.get,
+                latestKey: yield* query.latestKey.get,
+                latestFinalResult: yield* query.latestFinalResult.get,
+            }
+        })
+
+        const result = await runQueryTest(effect)
+
+        expect(calls).toBe(1)
+        expect(expectSuccessValue(result.final)).toBe("value:1:1")
+        expect(expectSomeValue(result.latestKey)).toEqual([1])
+        expect(expectSuccessValue(expectSomeValue(result.latestFinalResult))).toBe("value:1:1")
+    })
+})