add simple task model

app/src/main/java/ch/ost/rj/mge/miniproject/tasktracker/models/Task.kt

+package ch.ost.rj.mge.miniproject.tasktracker.models
+
+import java.util.*
+
+class Task {
+    var id: UUID = UUID.randomUUID()
+    var name: String? = null
+    var dueDate: Date? = null
+
+    var estimatedTimeMinutes: Long = 0
+    var actualTimeMinutes: Long = 0
+
+    fun differenceMinutes(): Long {
+        return this.actualTimeMinutes - this.estimatedTimeMinutes
+    }
+}

app/src/test/java/ch/ost/rj/mge/miniproject/tasktracker/models/TaskTest.kt

+package ch.ost.rj.mge.miniproject.tasktracker.models
+
+import org.junit.Test
+
+import org.junit.Assert.*
+
+class TaskTest {
+
+    @Test
+    fun difference_positive() {
+        val task = Task()
+        task.estimatedTimeMinutes = 10
+        task.actualTimeMinutes = 25
+        assertEquals(15, task.differenceMinutes())
+    }
+
+    @Test
+    fun difference_negative() {
+        val task = Task()
+        task.estimatedTimeMinutes = 25
+        task.actualTimeMinutes = 10
+        assertEquals(-15, task.differenceMinutes())
+    }
+}
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