mock pathname in vitest with nextjs

Lussy04

3 min read

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25-01-2025

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Testing Next.js applications with Vitest can be challenging when dealing with functionalities reliant on the routing system, particularly when involving pathnames. This article will guide you through effectively mocking pathname in Vitest for your Next.js projects, ensuring accurate and reliable unit tests. We'll cover several approaches, starting with the simplest and progressing to more sophisticated techniques.

Understanding the Challenge

Next.js's useRouter hook provides access to the current route information, including the pathname. Directly using useRouter within your component tests can lead to issues. Why? Because during testing, the router's context isn't available. Attempting to access useRouter().pathname directly within a Vitest test will yield an undefined value or an error.

Mocking Strategies

Here are several ways to handle pathname mocking in your tests, ranging from simple overrides to more comprehensive approaches:

1. Simple Direct Mocking (For Basic Cases)

If your component's behavior is directly tied to a specific pathname, a simple mock might suffice. This approach is best for less complex situations.

// my-component.test.ts
import { render, screen } from '@testing-library/react';
import MyComponent from './my-component';

test('renders correctly for /about pathname', () => {
  render(<MyComponent pathname="/about" />); //Directly pass in the pathname
  expect(screen.getByText('About Us')).toBeInTheDocument();
});

In this example, we directly pass the pathname prop to the component during rendering. This bypasses the need for useRouter entirely. This only works if your component accepts pathname as a prop.

2. Mocking useRouter with jest.spyOn (More Control)

For more complex scenarios, we can use jest.spyOn to mock the useRouter hook. This allows greater control over the mocked router object's behavior.

import { useRouter } from 'next/router';
import { render, screen } from '@testing-library/react';
import MyComponent from './my-component';
import { vi } from 'vitest'

vi.mock('next/router', () => ({
  useRouter: vi.fn(() => ({
    pathname: '/blog',
    route: '/blog',
    query: {},
    push: vi.fn(), //Mock the push function as well for completeness
    prefetch: vi.fn(),
  })),
}));

test('renders correctly for /blog pathname', () => {
    render(<MyComponent />);
    expect(screen.getByText('Blog Posts')).toBeInTheDocument();
});

Here, we mock the entire useRouter function to return a custom object, giving us complete control over its properties, including pathname. Remember to also mock any other methods of useRouter you are utilizing (like push or prefetch) to prevent further test errors.

3. Using a Mock Router Provider (Most Robust)

For the most comprehensive approach, consider creating a custom context provider that wraps your component and provides a mocked router context. This is especially useful when dealing with deeply nested components or complex routing logic.

// MockRouterProvider.tsx
import { createContext, useContext, ReactNode } from 'react';
import { useRouter } from 'next/router';

const RouterContext = createContext({ pathname: '', route: '' });

export const MockRouterProvider = ({ children, pathname = '/' , route = '/' }: { children: ReactNode; pathname?: string; route?: string}) => {
  return (
    <RouterContext.Provider value={{ pathname, route }}>
      {children}
    </RouterContext.Provider>
  );
};

export const useMockRouter = () => useContext(RouterContext);


// my-component.test.ts
import { render, screen } from '@testing-library/react';
import MyComponent from './my-component';
import { MockRouterProvider } from './MockRouterProvider';

test('renders correctly for /products pathname', () => {
  render(
    <MockRouterProvider pathname="/products">
      <MyComponent />
    </MockRouterProvider>
  );
  expect(screen.getByText('Our Products')).toBeInTheDocument();
});

This pattern provides a clean separation between your component and the mocking logic. It's more maintainable and easier to extend for more complex router interactions.

Choosing the Right Approach

The best mocking strategy depends on the complexity of your component and its interaction with the Next.js router. For simple scenarios, directly passing the pathname prop is sufficient. For more sophisticated tests, mocking useRouter or using a custom provider offers more control and maintainability. Remember to always strive for clear, concise, and reliable tests that accurately reflect your component's behavior. Thoroughly testing edge cases and different pathname scenarios is crucial for robust application stability.