ConnectApiHelperTest: "Context user does not have permission to create rich text in feed"

I installed the software from [UnofficialSF.com](https://unofficialsf.com/post-rich-chatter-invocable-action/) and when running unit tests, got this error

```
Class.ConnectApi.ChatterFeeds.postFeedElement: line 1458, column 1
Class.ConnectApiHelperTest.testCreateInputFromBody: line 257, column 1
10:18:52.130 (194554713)|FATAL_ERROR|ConnectApi.ConnectApiException: Context user does not have permission to create rich text in feed
```

The _ContextUser_ is `UserInfo.getUserId()` - which is me, user with System Admin profile. The test appears to be posting a bolded element.

test class is V47

`Network.getNetworkId()` returns null for the test context

What permission to I need to setup for the running user to be able to execute this unit test?