Skip to main content

Documentation Index

Fetch the complete documentation index at: https://mintlify.com/cloudflare/workers-sdk/llms.txt

Use this file to discover all available pages before exploring further.

Test your Workers using @cloudflare/vitest-pool-workers, which runs tests inside the actual workerd runtime for accurate results.

​
Why vitest-pool-workers?

Traditional testing frameworks run in Node.js, which has different APIs and behaviors than the Workers runtime. vitest-pool-workers runs your tests in the same workerd runtime as production, ensuring:
  • Accurate testing - Tests run in the actual Workers environment
  • Real bindings - Test with actual KV, R2, D1, Durable Objects implementations
  • Fast execution - Tests run directly in workerd without network overhead
  • Type safety - Full TypeScript support with runtime types

​
Installation

npm install -D vitest @cloudflare/vitest-pool-workers

​
Quick Start

1

Create vitest.config.ts

vitest.config.ts
import { defineWorkersConfig } from "@cloudflare/vitest-pool-workers/config";

export default defineWorkersConfig({
  test: {
    poolOptions: {
      workers: {
        wrangler: { configPath: "./wrangler.json" },
      },
    },
  },
});
2

Write your Worker

src/index.ts
export default {
  async fetch(request: Request, env: Env): Promise<Response> {
    const count = await env.KV.get("count") || "0";
    const newCount = parseInt(count) + 1;
    await env.KV.put("count", newCount.toString());
    return new Response(`Count: ${newCount}`);
  },
};
3

Write tests

src/index.test.ts
import { env, SELF } from "cloudflare:test";
import { describe, it, expect } from "vitest";

describe("Counter Worker", () => {
  it("increments count", async () => {
    const response = await SELF.fetch("http://example.com");
    expect(await response.text()).toBe("Count: 1");
  });

  it("persists across requests", async () => {
    await SELF.fetch("http://example.com");
    const response = await SELF.fetch("http://example.com");
    expect(await response.text()).toBe("Count: 2");
  });
});
4

Run tests

npx vitest

​
Configuration

​
Basic Configuration

vitest.config.ts
import { defineWorkersConfig } from "@cloudflare/vitest-pool-workers/config";

export default defineWorkersConfig({
  test: {
    poolOptions: {
      workers: {
        wrangler: {
          configPath: "./wrangler.json",
        },
      },
    },
  },
});

​
With Miniflare Options

vitest.config.ts
import { defineWorkersConfig } from "@cloudflare/vitest-pool-workers/config";

export default defineWorkersConfig({
  test: {
    poolOptions: {
      workers: {
        singleWorker: true,
        wrangler: {
          configPath: "./wrangler.json",
        },
        miniflare: {
          compatibilityFlags: ["nodejs_compat"],
          bindings: {
            TEST_MODE: "true",
          },
        },
      },
    },
  },
});

​
Multiple Workers

vitest.config.ts
import { defineWorkersConfig } from "@cloudflare/vitest-pool-workers/config";

export default defineWorkersConfig({
  test: {
    poolOptions: {
      workers: {
        main: "./src/index.ts",
        miniflare: {
          workers: [
            {
              name: "main-worker",
              modules: true,
              scriptPath: "./src/index.ts",
            },
            {
              name: "auth-worker",
              modules: true,
              scriptPath: "./src/auth.ts",
            },
          ],
        },
      },
    },
  },
});

​
Testing Patterns

​
Unit Tests

Test individual functions in isolation:
src/utils.test.ts
import { describe, it, expect } from "vitest";
import { parseJWT } from "./utils";

describe("parseJWT", () => {
  it("parses valid JWT", () => {
    const token = "eyJ...";
    const result = parseJWT(token);
    expect(result.userId).toBe("123");
  });

  it("throws on invalid JWT", () => {
    expect(() => parseJWT("invalid")).toThrow();
  });
});

​
Integration Tests

Test your Worker’s fetch handler:
src/index.test.ts
import { env, SELF } from "cloudflare:test";
import { describe, it, expect, beforeEach } from "vitest";

describe("API Worker", () => {
  beforeEach(async () => {
    // Clear KV before each test
    await env.KV.delete("user:123");
  });

  it("creates user", async () => {
    const response = await SELF.fetch("http://example.com/users", {
      method: "POST",
      body: JSON.stringify({ name: "Alice" }),
    });

    expect(response.status).toBe(201);
    const user = await response.json();
    expect(user.name).toBe("Alice");
  });

  it("retrieves user", async () => {
    await env.KV.put("user:123", JSON.stringify({ name: "Bob" }));

    const response = await SELF.fetch("http://example.com/users/123");
    expect(response.status).toBe(200);

    const user = await response.json();
    expect(user.name).toBe("Bob");
  });
});

​
Testing with Bindings

src/kv.test.ts
import { env } from "cloudflare:test";
import { describe, it, expect } from "vitest";

describe("KV Storage", () => {
  it("stores and retrieves values", async () => {
    await env.KV.put("key", "value");
    const result = await env.KV.get("key");
    expect(result).toBe("value");
  });

  it("supports JSON", async () => {
    const data = { name: "Alice", age: 30 };
    await env.KV.put("user", JSON.stringify(data));
    const result = await env.KV.get("user", "json");
    expect(result).toEqual(data);
  });

  it("lists keys", async () => {
    await env.KV.put("key1", "value1");
    await env.KV.put("key2", "value2");

    const list = await env.KV.list();
    expect(list.keys.length).toBeGreaterThanOrEqual(2);
  });
});

​
Testing Durable Objects

src/counter.test.ts
import { env, runInDurableObject } from "cloudflare:test";
import { describe, it, expect } from "vitest";

describe("Counter Durable Object", () => {
  it("increments count", async () => {
    const id = env.COUNTER.newUniqueId();
    const stub = env.COUNTER.get(id);

    const response1 = await stub.fetch("http://example.com/increment");
    expect(await response1.json()).toEqual({ count: 1 });

    const response2 = await stub.fetch("http://example.com/increment");
    expect(await response2.json()).toEqual({ count: 2 });
  });

  it("accesses internal state", async () => {
    const id = env.COUNTER.newUniqueId();

    const count = await runInDurableObject(env.COUNTER, id, async (instance) => {
      return instance.count;
    });

    expect(count).toBe(0);
  });
});

​
Testing D1 Databases

src/database.test.ts
import { env } from "cloudflare:test";
import { describe, it, expect, beforeAll } from "vitest";
import { applyD1Migrations } from "@cloudflare/vitest-pool-workers/config";
import migrations from "../migrations";

describe("Database", () => {
  beforeAll(async () => {
    await applyD1Migrations(env.DB, migrations);
  });

  it("inserts and queries users", async () => {
    await env.DB.prepare(
      "INSERT INTO users (name, email) VALUES (?, ?)"
    )
      .bind("Alice", "alice@example.com")
      .run();

    const result = await env.DB.prepare(
      "SELECT * FROM users WHERE name = ?"
    )
      .bind("Alice")
      .first();

    expect(result.name).toBe("Alice");
    expect(result.email).toBe("alice@example.com");
  });
});
With setup file:
test/setup.ts
import { env } from "cloudflare:test";
import { applyD1Migrations } from "@cloudflare/vitest-pool-workers/config";
import migrations from "../migrations";

export async function setup() {
  await applyD1Migrations(env.DB, migrations);
}
vitest.config.ts
import { defineWorkersConfig, readD1Migrations } from "@cloudflare/vitest-pool-workers/config";

export default defineWorkersConfig(async () => {
  const migrations = await readD1Migrations("./migrations");

  return {
    test: {
      setupFiles: ["./test/setup.ts"],
      poolOptions: {
        workers: {
          wrangler: { configPath: "./wrangler.json" },
          miniflare: {
            bindings: { TEST_MIGRATIONS: migrations },
          },
        },
      },
    },
  };
});

​
Testing Queues

src/queue.test.ts
import { env, getQueueResult, createMessageBatch } from "cloudflare:test";
import { describe, it, expect } from "vitest";
import worker from "./index";

describe("Queue Consumer", () => {
  it("processes messages", async () => {
    await env.MY_QUEUE.send({ userId: "123", action: "welcome" });

    const result = await getQueueResult(env.MY_QUEUE);
    expect(result.ackAll).toBe(true);
  });

  it("handles batch", async () => {
    const batch = await createMessageBatch(env.MY_QUEUE, [
      { userId: "1", action: "welcome" },
      { userId: "2", action: "welcome" },
    ]);

    await worker.queue(batch, env);
    expect(batch.messages.length).toBe(2);
  });
});

​
Testing Scheduled Events

src/cron.test.ts
import { env, createScheduledController } from "cloudflare:test";
import { describe, it, expect } from "vitest";
import worker from "./index";

describe("Scheduled Handler", () => {
  it("runs daily cleanup", async () => {
    const ctrl = createScheduledController({
      scheduledTime: new Date("2024-01-01T00:00:00Z"),
      cron: "0 0 * * *",
    });

    await worker.scheduled(ctrl, env, {} as ExecutionContext);

    // Verify cleanup ran
    const count = await env.KV.list();
    expect(count.keys.length).toBe(0);
  });
});

​
Mocking Fetch Requests

src/api.test.ts
import { env, fetchMock } from "cloudflare:test";
import { describe, it, expect, beforeAll, afterEach } from "vitest";
import worker from "./index";

describe("External API", () => {
  beforeAll(() => {
    fetchMock.activate();
    fetchMock.disableNetConnect();
  });

  afterEach(() => {
    fetchMock.assertNoPendingInterceptors();
  });

  it("fetches user data", async () => {
    fetchMock
      .get("https://api.example.com")
      .intercept({ path: "/users/123" })
      .reply(200, { name: "Alice", id: "123" });

    const response = await worker.fetch(
      new Request("http://example.com/user/123"),
      env,
      {} as ExecutionContext
    );

    const data = await response.json();
    expect(data.name).toBe("Alice");
  });

  it("handles errors", async () => {
    fetchMock
      .get("https://api.example.com")
      .intercept({ path: "/users/456" })
      .reply(404);

    const response = await worker.fetch(
      new Request("http://example.com/user/456"),
      env,
      {} as ExecutionContext
    );

    expect(response.status).toBe(404);
  });
});

​
Testing ExecutionContext

src/context.test.ts
import {
  env,
  createExecutionContext,
  waitOnExecutionContext,
} from "cloudflare:test";
import { describe, it, expect } from "vitest";
import worker from "./index";

describe("Execution Context", () => {
  it("waits for async tasks", async () => {
    const ctx = createExecutionContext();
    const request = new Request("http://example.com");

    const response = await worker.fetch(request, env, ctx);
    await waitOnExecutionContext(ctx);

    // All ctx.waitUntil() promises have resolved
    const result = await env.KV.get("processed");
    expect(result).toBe("true");
  });
});

​
Advanced Configuration

​
Isolated Storage

Each test file gets isolated storage by default. Enable singleWorker for shared storage:
vitest.config.ts
export default defineWorkersConfig({
  test: {
    poolOptions: {
      workers: {
        singleWorker: true,
        wrangler: { configPath: "./wrangler.json" },
      },
    },
  },
});

​
Environment-Specific Testing

vitest.config.ts
export default defineWorkersConfig({
  test: {
    poolOptions: {
      workers: {
        wrangler: {
          configPath: "./wrangler.json",
          environment: "staging",
        },
      },
    },
  },
});

​
Dynamic Configuration

vitest.config.ts
import { defineWorkersConfig } from "@cloudflare/vitest-pool-workers/config";

export default defineWorkersConfig(async ({ inject }) => {
  // Access values from globalSetup
  const port = inject("serverPort");

  return {
    test: {
      poolOptions: {
        workers: {
          wrangler: { configPath: "./wrangler.json" },
          miniflare: {
            bindings: {
              SERVER_PORT: port,
            },
          },
        },
      },
    },
  };
});

​
Global Setup

vitest.config.ts
import { defineWorkersConfig } from "@cloudflare/vitest-pool-workers/config";

export default defineWorkersConfig({
  test: {
    globalSetup: ["./test/global-setup.ts"],
    poolOptions: {
      workers: {
        wrangler: { configPath: "./wrangler.json" },
      },
    },
  },
});
test/global-setup.ts
import { provide } from "vitest/config";

export default async function () {
  const server = await startTestServer();

  provide("serverPort", server.port);

  return async () => {
    await server.close();
  };
}

​
Best Practices

​
1. Use Isolated Tests

Each test should be independent: 
import { beforeEach } from "vitest";

beforeEach(async () => {
  // Clear state before each test
  await env.KV.delete("key");
});

​
2. Test Edge Cases

it("handles missing data", async () => {
  const response = await SELF.fetch("http://example.com/user/999");
  expect(response.status).toBe(404);
});

it("handles malformed input", async () => {
  const response = await SELF.fetch("http://example.com/user/invalid");
  expect(response.status).toBe(400);
});

​
3. Use Type Safety

import type { Env } from "./types";

it("has correct types", ({ expect }) => {
  // TypeScript knows about env.KV, env.DB, etc.
  expect(env.KV).toBeDefined();
  expect(env.DB).toBeDefined();
});

​
4. Test Async Operations

it("completes async work", async () => {
  const ctx = createExecutionContext();

  const response = await worker.fetch(request, env, ctx);
  await waitOnExecutionContext(ctx);

  // All waitUntil promises completed
});

​
Troubleshooting

​
Tests Not Running

Ensure your pool is configured:
vitest.config.ts
export default defineWorkersConfig({
  test: {
    pool: "@cloudflare/vitest-pool-workers",
  },
});

​
Binding Not Available

Check your wrangler.json configuration and ensure bindings are defined.

​
Type Errors

Generate types: 
wrangler types
Then reference in your test: 
import type { Env } from "./worker-configuration";

​
Timeout Errors

Increase test timeout:
vitest.config.ts
export default defineWorkersConfig({
  test: {
    testTimeout: 30000,
  },
});

​
See Also

Local Development

Develop Workers locally with wrangler dev

Debugging

Debug Workers with DevTools

Vitest Documentation

Learn more about Vitest testing framework

Build docs developers (and LLMs) love

Get started for freeTalk to us