How to recreate this using sinon?

Below I have a test for express middleware. I'm looking to use sinon to mock these callbacks, rather then maintaining global state for thee variables.

  it('should return html', async () => {
    const val = []
    const req = {}
    const res = {send: (recieved) => {val.push(recieved)}}
    const next = (e) => {throw e}
    expect(val).to.be.length(0)
    await expressMiddleware(alpha)(req, res, next)
    const expectation = 'response sent'
    expect(val).to.be.length(1)
    expect(val[0]).to.be(expectation)
  })