add tests that will check env

```
// (this could also go in afterEach())
beforeEach(() => {
// Clear the Jest module cache
jest.resetModules();

// Clean up the environment
delete process.env.REACT_APP_BACKEND_HOST;
});

it('points to production', () => {
const config = setupTest('realsite.com');
expect(config.API_ROOT).toEqual('https://api.realsite.com/api/v1');
});

it('points to staging', () => {
const config = setupTest('staging.realsite.com');
expect(config.API_ROOT).toEqual('https://staging.api.realsite.com/api/v1');
});

it('points to QA', () => {
const config = setupTest('qa5.company.com');
expect(config.API_ROOT).toEqual('https://api.qa5.company.com/api/v1');
});

it('points to dev (default)', () => {
const config = setupTest('localhost');
expect(config.API_ROOT).toEqual('http://localhost:8080/api/v1');
});

it('points to dev (custom)', () => {
process.env.REACT_APP_BACKEND_HOST = 'custom';
const config = setupTest('localhost');
expect(config.API_ROOT).toEqual('custom/api/v1');
});

function setupTest(hostname) {
setHostname(hostname);
return require('./api-config');
}

// Set the global "hostname" property
// A simple "window.location.hostname = ..." won't work
function setHostname(hostname) {
Object.defineProperty(window.location, 'hostname', {
writable: true,
value: hostname
});
}
```

it's somekind important because env can be cashed, not sure if this is trouble to have big worries about, but tests are usually cool, so i want them