Mocking Environment Variables.md

import { beforeEach, expect, it } from 'vitest';

// you can reset it in beforeEach hook manually
const originalViteEnv = import.meta.env.VITE_ENV;

beforeEach(() => {
  import.meta.env.VITE_ENV = originalViteEnv;
});

it('changes value', () => {
  import.meta.env.VITE_ENV = 'staging';
  expect(import.meta.env.VITE_ENV).toBe('staging');
});

Here is a better way.

import { expect, it, vi } from 'vitest';

// before running tests "VITE_ENV" is "test"
import.meta.env.VITE_ENV === 'test';

it('changes value', () => {
  vi.stubEnv('VITE_ENV', 'staging');
  expect(import.meta.env.VITE_ENV).toBe('staging');
});

it('the value is restored before running an other test', () => {
  expect(import.meta.env.VITE_ENV).toBe('test');
});