testing-practices

This skill covers comprehensive testing strategies for modern JavaScript/TypeScript applications with Remix and SST.

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Install skill "testing-practices" with this command: npx skills add tejovanthn/rasikalife/tejovanthn-rasikalife-testing-practices

Testing Practices

This skill covers comprehensive testing strategies for modern JavaScript/TypeScript applications with Remix and SST.

Core Philosophy

Good tests are:

  • Fast: Run quickly to encourage frequent execution

  • Isolated: Each test is independent

  • Readable: Clear what's being tested and why

  • Reliable: Same input always produces same output

  • Maintainable: Easy to update when code changes

Testing Pyramid

 /\
/  \  E2E Tests (few)

/
/
/ Integr \ Integration Tests (some) /__
/
/ Unit \ Unit Tests (many) /__________\

Unit Tests (70%):

  • Test individual functions

  • Fast, isolated

  • Mock dependencies

Integration Tests (20%):

  • Test multiple components together

  • Test database queries

  • Test API routes

E2E Tests (10%):

  • Test full user workflows

  • Slow but high confidence

  • Critical paths only

Test Frameworks

Setup with Vitest

npm install -D vitest @vitest/ui

// vitest.config.ts import { defineConfig } from "vitest/config";

export default defineConfig({ test: { globals: true, environment: "node", setupFiles: ["./test/setup.ts"], coverage: { provider: "v8", reporter: ["text", "html"], exclude: ["/node_modules/", "/test/"] } } });

Setup for React/Remix

npm install -D @testing-library/react @testing-library/jest-dom @testing-library/user-event

// test/setup.ts import "@testing-library/jest-dom"; import { cleanup } from "@testing-library/react"; import { afterEach } from "vitest";

afterEach(() => { cleanup(); });

Unit Testing Patterns

Pattern 1: Testing Pure Functions

// src/lib/utils.ts export function calculateTotal(items: CartItem[]): number { return items.reduce((sum, item) => sum + item.price * item.quantity, 0); }

// test/lib/utils.test.ts import { describe, test, expect } from "vitest"; import { calculateTotal } from "../../src/lib/utils";

describe("calculateTotal", () => { test("returns 0 for empty cart", () => { expect(calculateTotal([])).toBe(0); });

test("calculates total for single item", () => { const items = [{ price: 10, quantity: 2 }]; expect(calculateTotal(items)).toBe(20); });

test("calculates total for multiple items", () => { const items = [ { price: 10, quantity: 2 }, { price: 5, quantity: 3 } ]; expect(calculateTotal(items)).toBe(35); });

test("handles decimal prices", () => { const items = [{ price: 9.99, quantity: 2 }]; expect(calculateTotal(items)).toBeCloseTo(19.98); }); });

Pattern 2: Testing with Mocks

// src/lib/email.ts import { SESClient, SendEmailCommand } from "@aws-sdk/client-ses";

export async function sendWelcomeEmail(email: string, name: string) { const ses = new SESClient({});

await ses.send(new SendEmailCommand({ Source: "noreply@example.com", Destination: { ToAddresses: [email] }, Message: { Subject: { Data: "Welcome!" }, Body: { Text: { Data: Hello ${name}! } } } })); }

// test/lib/email.test.ts import { describe, test, expect, vi } from "vitest"; import { sendWelcomeEmail } from "../../src/lib/email"; import { SESClient } from "@aws-sdk/client-ses";

vi.mock("@aws-sdk/client-ses", () => ({ SESClient: vi.fn(), SendEmailCommand: vi.fn() }));

describe("sendWelcomeEmail", () => { test("sends email with correct parameters", async () => { const mockSend = vi.fn().mockResolvedValue({}); (SESClient as any).mockImplementation(() => ({ send: mockSend }));

await sendWelcomeEmail("user@example.com", "John");

expect(mockSend).toHaveBeenCalledWith(
  expect.objectContaining({
    input: expect.objectContaining({
      Destination: { ToAddresses: ["user@example.com"] }
    })
  })
);

}); });

Pattern 3: Testing Async Functions

// src/lib/users.ts export async function getUser(id: string): Promise<User | null> { const result = await db.query({ TableName: Resource.Database.name, KeyConditionExpression: "pk = :pk", ExpressionAttributeValues: { ":pk": USER#${id} } });

return result.Items?.[0] as User | null; }

// test/lib/users.test.ts import { describe, test, expect, beforeEach, vi } from "vitest"; import { getUser } from "../../src/lib/users";

// Mock the database vi.mock("../../src/lib/db", () => ({ db: { query: vi.fn() } }));

import { db } from "../../src/lib/db";

describe("getUser", () => { beforeEach(() => { vi.clearAllMocks(); });

test("returns user when found", async () => { const mockUser = { pk: "USER#123", name: "John" }; (db.query as any).mockResolvedValue({ Items: [mockUser] });

const user = await getUser("123");
expect(user).toEqual(mockUser);

});

test("returns null when not found", async () => { (db.query as any).mockResolvedValue({ Items: [] });

const user = await getUser("123");
expect(user).toBeNull();

});

test("throws on database error", async () => { (db.query as any).mockRejectedValue(new Error("DB Error"));

await expect(getUser("123")).rejects.toThrow("DB Error");

}); });

Testing Remix Routes

Pattern 1: Testing Loaders

// app/routes/posts.$id.tsx export async function loader({ params }: LoaderFunctionArgs) { const post = await getPost(params.id); if (!post) { throw new Response("Not Found", { status: 404 }); } return json({ post }); }

// test/routes/posts.$id.test.ts import { describe, test, expect, vi } from "vitest"; import { loader } from "../../app/routes/posts.$id";

vi.mock("../../src/lib/posts", () => ({ getPost: vi.fn() }));

import { getPost } from "../../src/lib/posts";

describe("posts.$id loader", () => { test("returns post data when found", async () => { const mockPost = { id: "123", title: "Test Post" }; (getPost as any).mockResolvedValue(mockPost);

const response = await loader({
  params: { id: "123" },
  request: new Request("http://localhost/posts/123")
} as any);

const data = await response.json();
expect(data.post).toEqual(mockPost);

});

test("throws 404 when post not found", async () => { (getPost as any).mockResolvedValue(null);

await expect(
  loader({
    params: { id: "123" },
    request: new Request("http://localhost/posts/123")
  } as any)
).rejects.toThrow("Not Found");

}); });

Pattern 2: Testing Actions

// app/routes/posts.new.tsx export async function action({ request }: ActionFunctionArgs) { const formData = await request.formData(); const title = formData.get("title"); const content = formData.get("content");

if (!title || !content) { return json({ errors: { title: "Required", content: "Required" } }); }

const post = await createPost({ title, content }); return redirect(/posts/${post.id}); }

// test/routes/posts.new.test.ts import { describe, test, expect, vi } from "vitest"; import { action } from "../../app/routes/posts.new";

vi.mock("../../src/lib/posts", () => ({ createPost: vi.fn() }));

import { createPost } from "../../src/lib/posts";

describe("posts.new action", () => { test("creates post and redirects on success", async () => { const mockPost = { id: "123", title: "Test", content: "Content" }; (createPost as any).mockResolvedValue(mockPost);

const formData = new FormData();
formData.append("title", "Test");
formData.append("content", "Content");

const response = await action({
  request: new Request("http://localhost/posts/new", {
    method: "POST",
    body: formData
  })
} as any);

expect(response.status).toBe(302);
expect(response.headers.get("Location")).toBe("/posts/123");

});

test("returns errors for invalid data", async () => { const formData = new FormData(); formData.append("title", ""); formData.append("content", "");

const response = await action({
  request: new Request("http://localhost/posts/new", {
    method: "POST",
    body: formData
  })
} as any);

const data = await response.json();
expect(data.errors).toEqual({
  title: "Required",
  content: "Required"
});

}); });

Testing React Components

Pattern 1: Simple Component Tests

// app/components/PostCard.tsx export function PostCard({ post }: { post: Post }) { return ( <article> <h2>{post.title}</h2> <p>{post.content}</p> <time>{post.createdAt}</time> </article> ); }

// test/components/PostCard.test.tsx import { describe, test, expect } from "vitest"; import { render, screen } from "@testing-library/react"; import { PostCard } from "../../app/components/PostCard";

describe("PostCard", () => { test("renders post information", () => { const post = { id: "123", title: "Test Post", content: "This is content", createdAt: "2025-01-02" };

render(&#x3C;PostCard post={post} />);

expect(screen.getByText("Test Post")).toBeInTheDocument();
expect(screen.getByText("This is content")).toBeInTheDocument();
expect(screen.getByText("2025-01-02")).toBeInTheDocument();

}); });

Pattern 2: Interactive Components

// app/components/Counter.tsx import { useState } from "react";

export function Counter() { const [count, setCount] = useState(0);

return ( <div> <p>Count: {count}</p> <button onClick={() => setCount(count + 1)}>Increment</button> <button onClick={() => setCount(0)}>Reset</button> </div> ); }

// test/components/Counter.test.tsx import { describe, test, expect } from "vitest"; import { render, screen } from "@testing-library/react"; import userEvent from "@testing-library/user-event"; import { Counter } from "../../app/components/Counter";

describe("Counter", () => { test("increments count", async () => { const user = userEvent.setup(); render(<Counter />);

expect(screen.getByText("Count: 0")).toBeInTheDocument();

await user.click(screen.getByText("Increment"));
expect(screen.getByText("Count: 1")).toBeInTheDocument();

await user.click(screen.getByText("Increment"));
expect(screen.getByText("Count: 2")).toBeInTheDocument();

});

test("resets count", async () => { const user = userEvent.setup(); render(<Counter />);

await user.click(screen.getByText("Increment"));
await user.click(screen.getByText("Increment"));
expect(screen.getByText("Count: 2")).toBeInTheDocument();

await user.click(screen.getByText("Reset"));
expect(screen.getByText("Count: 0")).toBeInTheDocument();

}); });

Testing SST Functions

Pattern 1: Testing Lambda Handlers

// src/api/posts.ts import { APIGatewayProxyEventV2, APIGatewayProxyResultV2 } from "aws-lambda"; import { getPosts } from "../lib/posts";

export async function handler( event: APIGatewayProxyEventV2 ): Promise<APIGatewayProxyResultV2> { const posts = await getPosts();

return { statusCode: 200, body: JSON.stringify({ posts }) }; }

// test/api/posts.test.ts import { describe, test, expect, vi } from "vitest"; import { handler } from "../../src/api/posts";

vi.mock("../../src/lib/posts", () => ({ getPosts: vi.fn() }));

import { getPosts } from "../../src/lib/posts";

describe("posts handler", () => { test("returns posts", async () => { const mockPosts = [{ id: "1", title: "Post 1" }]; (getPosts as any).mockResolvedValue(mockPosts);

const result = await handler({} as any);

expect(result.statusCode).toBe(200);
expect(JSON.parse(result.body!)).toEqual({ posts: mockPosts });

});

test("handles errors", async () => { (getPosts as any).mockRejectedValue(new Error("DB Error"));

const result = await handler({} as any);

expect(result.statusCode).toBe(500);

}); });

Integration Testing

Pattern 1: Testing with Real Database

// test/integration/posts.test.ts import { describe, test, expect, beforeAll, afterAll } from "vitest"; import { DynamoDBClient } from "@aws-sdk/client-dynamodb"; import { DynamoDBDocumentClient } from "@aws-sdk/lib-dynamodb"; import { createPost, getPost } from "../../src/lib/posts";

// Use local DynamoDB for tests const client = DynamoDBDocumentClient.from( new DynamoDBClient({ endpoint: "http://localhost:8000" }) );

describe("Post operations", () => { beforeAll(async () => { // Create test table await createTestTable(); });

afterAll(async () => { // Clean up test table await deleteTestTable(); });

test("creates and retrieves post", async () => { const postData = { title: "Test Post", content: "This is a test", authorId: "user123" };

const created = await createPost(postData);
expect(created.id).toBeDefined();
expect(created.title).toBe(postData.title);

const retrieved = await getPost(created.id);
expect(retrieved).toEqual(created);

}); });

E2E Testing with Playwright

// e2e/auth.spec.ts import { test, expect } from "@playwright/test";

test("user can sign up and log in", async ({ page }) => { // Sign up await page.goto("/signup"); await page.fill('input[name="email"]', "test@example.com"); await page.fill('input[name="password"]', "password123"); await page.fill('input[name="name"]', "Test User"); await page.click('button[type="submit"]');

// Should redirect to dashboard await expect(page).toHaveURL("/dashboard"); await expect(page.locator("text=Welcome, Test User")).toBeVisible();

// Log out await page.click('button:has-text("Log out")'); await expect(page).toHaveURL("/");

// Log in await page.goto("/login"); await page.fill('input[name="email"]', "test@example.com"); await page.fill('input[name="password"]', "password123"); await page.click('button[type="submit"]');

// Should be logged in await expect(page).toHaveURL("/dashboard"); });

Test Best Practices

  1. Use Descriptive Test Names

✅ Do:

test("returns 404 when post not found", () => {}); test("creates user and sends welcome email", () => {});

❌ Don't:

test("test1", () => {}); test("works", () => {});

  1. Follow AAA Pattern

test("updates post title", async () => { // Arrange const post = await createPost({ title: "Old Title" });

// Act await updatePost(post.id, { title: "New Title" });

// Assert const updated = await getPost(post.id); expect(updated.title).toBe("New Title"); });

  1. Test One Thing Per Test

✅ Do:

test("validates email format", () => {}); test("validates email uniqueness", () => {});

❌ Don't:

test("validates email", () => { // Tests 5 different things });

  1. Mock External Dependencies

// Mock AWS services vi.mock("@aws-sdk/client-s3");

// Mock environment variables vi.stubEnv("API_KEY", "test-key");

// Mock time vi.useFakeTimers(); vi.setSystemTime(new Date("2025-01-02"));

  1. Clean Up After Tests

import { afterEach, beforeEach } from "vitest";

beforeEach(() => { // Set up test data });

afterEach(() => { // Clean up vi.clearAllMocks(); vi.restoreAllMocks(); });

Coverage Goals

Aim for:

  • Unit tests: 80%+ coverage

  • Integration tests: Key workflows

  • E2E tests: Critical user paths

Run tests with coverage

npm test -- --coverage

Set minimum coverage

vitest.config.ts: coverage: { lines: 80, functions: 80, branches: 75, statements: 80 }

CI/CD Integration

.github/workflows/test.yml

name: Test

on: [push, pull_request]

jobs: test: runs-on: ubuntu-latest steps: - uses: actions/checkout@v3 - uses: actions/setup-node@v3 - run: npm install - run: npm test - run: npm run test:e2e

Further Reading

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