B2BUtils tests - inserting WebStoreNetwork

I'm trying to create a test for `B2BUtils.resolveCommunityIdToWebstoreId` and am running into problems creating the WebStoreNetwork in my @testSetup

```
@isTest
private class B2BUtilsTest {
@testSetup static void setup() {
WebStore testWebStore = new WebStore(Name='TestWebStore', DefaultLanguage='en_US');
insert testWebStore;

WebStoreNetwork testWebStoreNetwork = new WebStoreNetwork(WebStoreId=testWebStore.Id);
insert testWebStoreNetwork;
}
```

In the Developer Console, I see the following errors:
* `Field is not writeable: WebStoreNetwork.WebStoreId`
* `DML operation Insert not allowed on WebStoreNetwork`

I extremely new to Salesforce development and apologize if this problem has an obvious solution. I'm not able to find any documentation on the WebStoreNetwork object or how to create one.

On a side note, if this repo is really intended to be a quickstart, it seems like a bare minimum requirement would be 75% test coverage on the included utility classes. Currently, there are at least four classes that have no tests whatsoever: B2BCartToOrderDraft, B2BGetInfo, B2BUtils and SalesforceAdapter

Start with B2BUtils.resolveCommunityIdToWebstoreId and the B2BUtilsTest @testSetup shown in the issue. Investigate the documented creation and testing constraints for WebStoreNetwork, then determine how the test data can be provided. Done means the test setup runs without the reported field-writeability or insert errors.

Written by the indexing model from the issue text.