NPE when stubbing a mock's method with Mockito - unit-testing

Question

I am trying to test a repository ExpensesRepository
class ExpensesRepository #Inject constructor(
private val store: DataStore
) : AbstractRepository<Expense> {
override fun get(offset: Int, limit: Int): List<Expense?> =
store.getAll(offset, limit)
override fun get(key: String): Expense? = store.getOne(key = key)
override fun create(input: Expense) =
store.create(key = input.key, element = input)
override fun delete(key: String) = store.remove(key = key)
override fun update(
key: String,
update: Expense
): Expense =
store.update(key = key, element = update)
override fun removeAll() = store.flush()
}
In the test suite I have mocked the store parameter using mockito, then I stubbed that mock's method getOne(String) to return an expense object from my fixtures.
Here is my test suite
class ExpensesRepositoryTest {
#get:Rule
var instantTaskExecutorRule = InstantTaskExecutorRule()
private lateinit var repository: ExpensesRepository
private val dataStore = mock<DataStore>()
private val expense = Expense(
"key",
1,
"name",
"date",
12.12
)
private val expenseList = listOf(
expense,
expense,
expense
)
private val dummyKey = "expense_key"
#Before
fun setup() {
repository = ExpensesRepository(dataStore)
}
#Test
fun `should get an item with existing key`() {
whenever(dataStore.getOne<Expense>(dummyKey)).thenReturn(expense)
val result = repository.get(dummyKey)
verify(dataStore, Times(1)).getOne<Expense>(dummyKey)
assertThat(result).isEqualTo(expense)
}
}
When I run the test it fails cuz of NullPointerException and that's when the DataStore calls the function getOne(String) that I supposedly stubbed earlier. In case it helps here is the DataStore class
class DataStore(val store: Persistence, val gson: Gson) {
inline fun <reified R : Persistable> getAll(
offset: Int,
limit: Int
): List<R?> =
store.get(offset, limit).map { it.maybeMapTo<R>(mapper = gson) }
inline fun <reified R : Persistable> getOne(key: String): R? =
store.get(key).maybeMapTo<R>(mapper = gson)
fun create(key: String, element: Persistable) {
store.create(
key = key,
element = when (store) {
is JsonBased -> gson.toJson(element)
else -> element
}
)
}
inline fun <reified R : Persistable> update(
key: String,
element: R
): R {
return store.update(key, element) as R
}
fun remove(key: String) {
store.remove(key)
}
fun flush() {
store.flush()
}
}
Is there something I am doing wrong here?

Answer 1

I'm afraid you are out of luck: inline functions are not mockable.