Make usecases generic

Author: Gerrit Garbereder

Task-Tracker-Usecases/src/commonMain/kotlin/com/garbereder/tasktracker/usecases/UseCase.kt

@@ -1,5 +1,5 @@
 package com.garbereder.tasktracker.usecases
 
-interface UseCase {
-    fun invoke()
+interface UseCase<out T> {
+    fun invoke(): T
 }

Task-Tracker-Usecases/src/commonMain/kotlin/com/garbereder/tasktracker/usecases/tasks/AddTask.kt

@@ -4,6 +4,6 @@ import com.garbereder.tasktracker.entities.Task
 import com.garbereder.tasktracker.entities.TaskCollection
 import com.garbereder.tasktracker.usecases.UseCase
 
-class AddTask constructor(private val collection: TaskCollection, private val task: Task) : UseCase {
-    override fun invoke() = collection.add(task)
+class AddTask constructor(private val collection: TaskCollection, private val taskName: String) : UseCase<Unit> {
+    override fun invoke() = collection.add(Task("${collection.size() + 1}", taskName))
 }

Task-Tracker-Usecases/src/commonMain/kotlin/com/garbereder/tasktracker/usecases/tasks/LoadTasks.kt

@@ -3,12 +3,6 @@ package com.garbereder.tasktracker.usecases.tasks
 import com.garbereder.tasktracker.entities.TaskCollection
 import com.garbereder.tasktracker.usecases.UseCase
 
-class LoadTasks(private val reader: TaskCollectionReader) : UseCase {
-
-    lateinit var tasks: TaskCollection
-
-    override fun invoke() {
-        tasks = this.reader.read()
-    }
-
+class LoadTasks(private val reader: TaskCollectionReader) : UseCase<TaskCollection> {
+    override fun invoke(): TaskCollection = this.reader.read()
 }

Task-Tracker-Usecases/src/commonMain/kotlin/com/garbereder/tasktracker/usecases/tasks/RemoveTask.kt

@@ -4,6 +4,6 @@ import com.garbereder.tasktracker.entities.Task
 import com.garbereder.tasktracker.entities.TaskCollection
 import com.garbereder.tasktracker.usecases.UseCase
 
-class RemoveTask(private val collection: TaskCollection, private val task: Task): UseCase {
+class RemoveTask(private val collection: TaskCollection, private val task: Task): UseCase<Unit> {
     override fun invoke() = collection.remove(task)
 }

Task-Tracker-Usecases/src/commonMain/kotlin/com/garbereder/tasktracker/usecases/tasks/TaskCollectionFactory.kt

@@ -5,18 +5,22 @@ import com.garbereder.tasktracker.entities.TaskCollection
 import io.mockative.*
 import kotlin.test.*
 
-class AddTaskTes {
+class AddTaskTests {
     @Mock
     val collection = mock(classOf<TaskCollection>())
 
     @Test
     fun invoke_noInput_callsThrough() {
-        val task = Task("TaskId", "TaskName")
+        val task = Task("1","TaskName")
         given(collection).invocation { add(task) }
             .thenDoNothing()
+        given(collection).invocation { size() }
+            .then { 0 }
 
-        AddTask(collection, task).invoke()
+        AddTask(collection, "TaskName").invoke()
 
+        verify(collection).invocation { size() }
+            .wasInvoked(exactly = once)
         verify(collection).invocation { add(task) }
             .wasInvoked(exactly = once)
     }

Task-Tracker-Usecases/src/commonTest/kotlin/com/garbereder/tasktracker/usecases/tasks/AddTaskTest.kt

@@ -5,6 +5,7 @@ import com.garbereder.tasktracker.entities.TaskCollection
 import com.garbereder.tasktracker.usecases.UseCase
 import io.mockative.*
 import kotlin.test.Test
+import kotlin.test.assertEquals
 import kotlin.test.assertNotNull
 import kotlin.test.assertTrue
 
@@ -18,7 +19,8 @@ class LoadTasksTests {
         given(reader).invocation { read() }
             .then { collection }
 
-        LoadTasks(reader).invoke()
+        val col = LoadTasks(reader).invoke()
+        assertEquals(collection, col)
 
         verify(reader).invocation { read() }
             .wasInvoked(exactly = once)