Different NODE_ENV for different tests

Question

I am testing my API with supertest

I want to check if my CSRF marker protection works, and then disable it for other tests.

For this, I installed NODE_ENVin testornot_test

app.js

var csrf = require('csurf');   
var app  = express();
if (process.env.NODE_ENV !== 'test') {
  app.use(csrf({ cookie: true }));
  app.use(function(req, res, next) {
    res.cookie('XSRF-TOKEN', req.csrfToken());
    return next();
  });
}

CSRF test

process.env.NODE_ENV = 'not_test';

var app = require("app.js");
var request = require('supertest')(app);

var testAccount = {
  "login": "test",
  "pass": "test"
};

describe('CSRF protection', function() {
  it('On /login', function(done){
    request
      .post('/login')
      .send(testAccount)
      .expect(403, done);
  });
});

Test login NODE_ENV is now being tested

process.env.NODE_ENV = 'test';

var app = require("app.js");
var request = require('supertest').agent(app);

var testAccount = {
  "login": "test",
  "pass": "test"
};

describe('API Admin roads', function() {
  before(function (done) {
    request
      .post('/login')
      .send(testAccount)
      .end(done);
  });

  it('/api/admin/groups/', function(done){
    request
      .get('/api/admin/groups/')
      .expect(200, done);
  });
});

The problem is that only the first is taken into account process.env.NODE_ENV, if I install it on not_test, and then on test, I will still be in not_test.