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Testing Guide

How to test components that use Dropup.

Setup​

Install testing dependencies:

npm install -D vitest @testing-library/react @testing-library/user-event jsdom

Configure Vitest:

// vitest.config.ts
import { defineConfig } from 'vitest/config';
import react from '@vitejs/plugin-react';

export default defineConfig({
  plugins: [react()],
  test: {
    environment: 'jsdom',
    setupFiles: './src/test/setup.ts',
  },
});
// src/test/setup.ts
import '@testing-library/jest-dom';

Basic Component Test​

// components/Uploader.tsx
import { useDropup } from '@samithahansaka/dropup';

export function Uploader() {
  const { files, getDropProps, getInputProps } = useDropup({
    accept: 'image/*',
  });

  return (
    <div {...getDropProps()} data-testid="dropzone">
      <input {...getInputProps()} data-testid="file-input" />
      <p>Drop images here</p>

      <ul data-testid="file-list">
        {files.map(file => (
          <li key={file.id} data-testid="file-item">
            {file.name}
          </li>
        ))}
      </ul>
    </div>
  );
}
// components/Uploader.test.tsx
import { render, screen } from '@testing-library/react';
import userEvent from '@testing-library/user-event';
import { describe, it, expect } from 'vitest';
import { Uploader } from './Uploader';

describe('Uploader', () => {
  it('renders dropzone', () => {
    render(<Uploader />);
    expect(screen.getByTestId('dropzone')).toBeInTheDocument();
    expect(screen.getByText('Drop images here')).toBeInTheDocument();
  });

  it('accepts file input', async () => {
    const user = userEvent.setup();
    render(<Uploader />);

    const input = screen.getByTestId('file-input');
    const file = new File(['test'], 'test.png', { type: 'image/png' });

    await user.upload(input, file);

    expect(screen.getByTestId('file-item')).toHaveTextContent('test.png');
  });

  it('accepts multiple files', async () => {
    const user = userEvent.setup();
    render(<Uploader />);

    const input = screen.getByTestId('file-input');
    const files = [
      new File(['test1'], 'photo1.png', { type: 'image/png' }),
      new File(['test2'], 'photo2.png', { type: 'image/png' }),
    ];

    await user.upload(input, files);

    const items = screen.getAllByTestId('file-item');
    expect(items).toHaveLength(2);
  });
});

Testing Drag and Drop​

import { render, screen, fireEvent } from '@testing-library/react';
import { describe, it, expect } from 'vitest';
import { Uploader } from './Uploader';

describe('Drag and Drop', () => {
  it('shows drag state when dragging over', () => {
    render(<Uploader />);

    const dropzone = screen.getByTestId('dropzone');

    fireEvent.dragEnter(dropzone, {
      dataTransfer: {
        types: ['Files'],
        items: [{ kind: 'file' }],
      },
    });

    expect(dropzone).toHaveAttribute('data-dragging', 'true');
  });

  it('handles file drop', () => {
    render(<Uploader />);

    const dropzone = screen.getByTestId('dropzone');
    const file = new File(['test'], 'dropped.png', { type: 'image/png' });

    fireEvent.drop(dropzone, {
      dataTransfer: {
        files: [file],
        types: ['Files'],
      },
    });

    expect(screen.getByText('dropped.png')).toBeInTheDocument();
  });
});

Testing Validation​

// components/ValidatedUploader.tsx
import { useDropup } from '@samithahansaka/dropup';
import { useState } from 'react';

export function ValidatedUploader() {
  const [errors, setErrors] = useState<string[]>([]);

  const { files, getDropProps, getInputProps } = useDropup({
    accept: 'image/*',
    maxSize: 1024 * 1024, // 1MB

    onValidationError: (validationErrors) => {
      const messages = validationErrors.flatMap(e => e.errors);
      setErrors(messages);
    },
  });

  return (
    <div {...getDropProps()} data-testid="dropzone">
      <input {...getInputProps()} data-testid="file-input" />

      {errors.length > 0 && (
        <ul data-testid="error-list">
          {errors.map((error, i) => (
            <li key={i} data-testid="error-item">{error}</li>
          ))}
        </ul>
      )}
    </div>
  );
}
// components/ValidatedUploader.test.tsx
import { render, screen } from '@testing-library/react';
import userEvent from '@testing-library/user-event';
import { describe, it, expect } from 'vitest';
import { ValidatedUploader } from './ValidatedUploader';

describe('Validation', () => {
  it('rejects wrong file type', async () => {
    const user = userEvent.setup();
    render(<ValidatedUploader />);

    const input = screen.getByTestId('file-input');
    const file = new File(['test'], 'document.pdf', { type: 'application/pdf' });

    await user.upload(input, file);

    expect(screen.getByTestId('error-list')).toBeInTheDocument();
  });

  it('rejects files over size limit', async () => {
    const user = userEvent.setup();
    render(<ValidatedUploader />);

    const input = screen.getByTestId('file-input');
    // Create a 2MB file (over 1MB limit)
    const content = new Array(2 * 1024 * 1024).fill('a').join('');
    const file = new File([content], 'large.png', { type: 'image/png' });

    await user.upload(input, file);

    expect(screen.getByTestId('error-list')).toBeInTheDocument();
  });
});

Testing Upload​

// components/UploadingComponent.tsx
import { useDropup } from '@samithahansaka/dropup';

export function UploadingComponent() {
  const { files, actions, state, getDropProps, getInputProps } = useDropup({
    upload: { url: '/api/upload' },
  });

  return (
    <div {...getDropProps()} data-testid="dropzone">
      <input {...getInputProps()} data-testid="file-input" />

      {files.map(file => (
        <div key={file.id} data-testid="file-status">
          {file.status === 'uploading' && `Uploading: ${file.progress}%`}
          {file.status === 'complete' && 'Done!'}
          {file.status === 'error' && `Error: ${file.error?.message}`}
        </div>
      ))}

      <button
        onClick={() => actions.upload()}
        disabled={state.isUploading}
        data-testid="upload-btn"
      >
        Upload
      </button>
    </div>
  );
}
// components/UploadingComponent.test.tsx
import { render, screen, waitFor } from '@testing-library/react';
import userEvent from '@testing-library/user-event';
import { describe, it, expect, vi, beforeEach } from 'vitest';
import { UploadingComponent } from './UploadingComponent';

// Mock fetch
const mockFetch = vi.fn();
global.fetch = mockFetch;

describe('Upload', () => {
  beforeEach(() => {
    mockFetch.mockReset();
  });

  it('uploads files successfully', async () => {
    mockFetch.mockResolvedValue({
      ok: true,
      json: () => Promise.resolve({ url: 'https://example.com/file.png' }),
    });

    const user = userEvent.setup();
    render(<UploadingComponent />);

    // Add file
    const input = screen.getByTestId('file-input');
    const file = new File(['test'], 'test.png', { type: 'image/png' });
    await user.upload(input, file);

    // Click upload
    await user.click(screen.getByTestId('upload-btn'));

    // Wait for completion
    await waitFor(() => {
      expect(screen.getByTestId('file-status')).toHaveTextContent('Done!');
    });

    expect(mockFetch).toHaveBeenCalledWith('/api/upload', expect.anything());
  });

  it('handles upload error', async () => {
    mockFetch.mockRejectedValue(new Error('Network error'));

    const user = userEvent.setup();
    render(<UploadingComponent />);

    const input = screen.getByTestId('file-input');
    await user.upload(input, new File(['test'], 'test.png', { type: 'image/png' }));

    await user.click(screen.getByTestId('upload-btn'));

    await waitFor(() => {
      expect(screen.getByTestId('file-status')).toHaveTextContent('Error');
    });
  });
});

Mocking useDropup​

For isolated unit tests:

// __mocks__/@samithahansaka/dropup.ts
import { vi } from 'vitest';

export const useDropup = vi.fn(() => ({
  files: [],
  state: {
    isDragging: false,
    isDragAccept: false,
    isDragReject: false,
    isUploading: false,
    progress: 0,
    status: 'idle',
  },
  actions: {
    upload: vi.fn(),
    cancel: vi.fn(),
    remove: vi.fn(),
    reset: vi.fn(),
    retry: vi.fn(),
    addFiles: vi.fn(),
    updateFileMeta: vi.fn(),
  },
  getDropProps: vi.fn(() => ({})),
  getInputProps: vi.fn(() => ({ type: 'file' })),
  openFileDialog: vi.fn(),
}));
// Usage in tests
import { vi } from 'vitest';
import { useDropup } from '@samithahansaka/dropup';

vi.mock('@samithahansaka/dropup');

const mockUseDropup = vi.mocked(useDropup);

describe('With mocked hook', () => {
  it('renders with files', () => {
    mockUseDropup.mockReturnValue({
      files: [
        { id: '1', name: 'test.png', status: 'idle', progress: 0, size: 1000, type: 'image/png' },
      ],
      // ... other values
    });

    render(<Uploader />);
    expect(screen.getByText('test.png')).toBeInTheDocument();
  });
});

Testing with MSW​

Use Mock Service Worker for realistic API testing:

// src/test/handlers.ts
import { http, HttpResponse } from 'msw';

export const handlers = [
  http.post('/api/upload', async ({ request }) => {
    const formData = await request.formData();
    const file = formData.get('file') as File;

    return HttpResponse.json({
      url: `https://example.com/uploads/${file.name}`,
    });
  }),

  http.post('/api/upload-error', () => {
    return HttpResponse.json(
      { error: 'Upload failed' },
      { status: 500 }
    );
  }),
];
// src/test/setup.ts
import { setupServer } from 'msw/node';
import { handlers } from './handlers';

export const server = setupServer(...handlers);

beforeAll(() => server.listen());
afterEach(() => server.resetHandlers());
afterAll(() => server.close());

E2E Testing with Playwright​

// e2e/upload.spec.ts
import { test, expect } from '@playwright/test';

test.describe('File Upload', () => {
  test('uploads a file', async ({ page }) => {
    await page.goto('/upload');

    // Get the file input
    const fileInput = page.locator('input[type="file"]');

    // Upload file
    await fileInput.setInputFiles({
      name: 'test.png',
      mimeType: 'image/png',
      buffer: Buffer.from('fake image content'),
    });

    // Verify file appears in list
    await expect(page.locator('text=test.png')).toBeVisible();

    // Click upload button
    await page.click('button:has-text("Upload")');

    // Wait for success
    await expect(page.locator('text=Done')).toBeVisible();
  });

  test('drag and drop upload', async ({ page }) => {
    await page.goto('/upload');

    const dropzone = page.locator('[data-testid="dropzone"]');

    // Create file data
    const buffer = Buffer.from('test content');

    // Simulate drag and drop
    const dataTransfer = await page.evaluateHandle(() => new DataTransfer());

    await page.dispatchEvent('[data-testid="dropzone"]', 'drop', {
      dataTransfer,
    });

    // Verify file added
    await expect(page.locator('[data-testid="file-item"]')).toBeVisible();
  });
});

Best Practices​

  1. Test behavior, not implementation - Focus on what users see and do
  2. Use data-testid for reliability - Avoid testing by CSS classes
  3. Mock network requests - Use MSW or vi.mock for API calls
  4. Test edge cases - Empty states, errors, large files
  5. Test accessibility - Keyboard navigation, screen readers