I am new to Kotlin and I am writing unit test for a method that tries to load a value from a map defined at class level (kind of like a local cache) and returns if the value is found otherwise a custom exception. I am having a hard time imagining how to do that.

I am using org.mockito.kotlin.whenever to mock responses by other methods but not sure what i need to do in this case ?
Would appreciate the help and sorry if its a very basic question

I can’t think of a solution so would appreciate any pointers.

The code roughly looks like below. I am trying to write the tests for fetch() method and load()

class Original { 
    private val cache = mutableMapOf<String,ClassAbc>()

    // loads the value from cache and if not present then calls api and saves to cache
    fun load(){
        fetch()?. run{
  
          cache["abc"]=callApi()
        }
    }

    fun fetch(key: String) : Map<String, ClassAbc> {
        // fetches the values from cache and returns an empty map if not found
        finalMap = mutableMapOf<String, ClassAbc>()
        cache[key]?.let {
            finalMap[key] = it
        }

        return finalMap
}