Unit test for a method that populates a dictionary from an API call
There is a better way than using a string, there is a Namespace that you can import called Json or System.Json

after you have imported this you have access to JsonValue Arrays which allows you to nest JavaScript Objects creating a JSON Document.

it actually looks like you are already using the Namespace to deserialize the string into an object, not sure why you aren't just creating the JSON Objects themselves. they are just collections of KeyValuePairs of Of String, JsonValue  (Dictionaries, Collections, or Enumerables)