next.js/test/unit/isolated/config.test.ts

/* eslint-env jest */
import { join } from 'path'
import { PHASE_DEVELOPMENT_SERVER } from 'next/constants'

const pathToConfig = join(__dirname, '_resolvedata', 'without-function')
const pathToConfigFn = join(__dirname, '_resolvedata', 'with-function')

// force require usage instead of dynamic import in jest
// x-ref: https://github.com/nodejs/node/issues/35889
process.env.__NEXT_TEST_MODE = 'jest'

describe('config', () => {
  let loadConfig: typeof import('next/dist/server/config').default

  beforeEach(async () => {
    // Reset the module cache to ensure each test gets a fresh config load
    // This is important because config.ts now has a module-level configCache
    jest.resetModules()

    // Dynamically import the module after reset to get a fresh instance
    const configModule = await import('next/dist/server/config')
    loadConfig = configModule.default
  })
  it('Should get the configuration', async () => {
    const config = await loadConfig(PHASE_DEVELOPMENT_SERVER, pathToConfig)
    expect(config.customConfig).toBe(true)
  })

  it('Should pass the phase correctly', async () => {
    const config = await loadConfig(PHASE_DEVELOPMENT_SERVER, pathToConfigFn)
    expect(config.phase).toBe(PHASE_DEVELOPMENT_SERVER)
  })

  it('Should pass the defaultConfig correctly', async () => {
    const config = await loadConfig(PHASE_DEVELOPMENT_SERVER, pathToConfigFn)
    expect(config.defaultConfig).toBeDefined()
  })

  it('Should assign object defaults deeply to user config', async () => {
    const config = await loadConfig(PHASE_DEVELOPMENT_SERVER, pathToConfigFn)
    expect(config.distDir).toEqual('.next')
    expect(config.onDemandEntries.maxInactiveAge).toBeDefined()
  })

  it('Should pass the customConfig correctly', async () => {
    const config = await loadConfig(PHASE_DEVELOPMENT_SERVER, '<rootDir>', {
      customConfig: {
        customConfigKey: 'customConfigValue',
      },
    })
    expect(config.customConfigKey).toBe('customConfigValue')
  })

  it('Should assign object defaults deeply to customConfig', async () => {
    const config = await loadConfig(PHASE_DEVELOPMENT_SERVER, '<rootDir>', {
      customConfig: {
        customConfig: true,
        onDemandEntries: { custom: true },
      },
    })
    expect(config.customConfig).toBe(true)
    expect(config.onDemandEntries.maxInactiveAge).toBeDefined()
  })

  it('Should allow setting objects which do not have defaults', async () => {
    const config = await loadConfig(PHASE_DEVELOPMENT_SERVER, '<rootDir>', {
      customConfig: {
        bogusSetting: { custom: true },
      },
    })
    expect(config.bogusSetting).toBeDefined()
    expect(config.bogusSetting.custom).toBe(true)
  })

  it('Should override defaults for arrays from user arrays', async () => {
    const config = await loadConfig(PHASE_DEVELOPMENT_SERVER, '<rootDir>', {
      customConfig: {
        pageExtensions: ['.bogus'],
      },
    })
    expect(config.pageExtensions).toEqual(['.bogus'])
  })

  it('Should throw when an invalid target is provided', async () => {
    await expect(async () => {
      await loadConfig(
        PHASE_DEVELOPMENT_SERVER,
        join(__dirname, '_resolvedata', 'invalid-target')
      )
    }).rejects.toThrow(/The "target" property is no longer supported/)
  })

  it('Should throw an error when next.config.(js | mjs | ts) is not present', async () => {
    await expect(
      async () =>
        await loadConfig(
          PHASE_DEVELOPMENT_SERVER,
          join(__dirname, '_resolvedata', 'missing-config')
        )
    ).rejects.toThrow(
      /Configuring Next.js via .+ is not supported. Please replace the file with 'next.config.js'/
    )
  })

  it('Should not throw an error when two versions of next.config.js are present', async () => {
    const config = await loadConfig(
      PHASE_DEVELOPMENT_SERVER,
      join(__dirname, '_resolvedata', 'js-ts-config')
    )
    expect(config.__test__ext).toBe('js')
  })

  it('Should not throw an error when next.config.ts is present', async () => {
    const config = await loadConfig(
      PHASE_DEVELOPMENT_SERVER,
      join(__dirname, '_resolvedata', 'typescript-config')
    )
    expect(config.__test__ext).toBe('ts')
  })
})