Show completed task feature (#5)

This PR contains the work done to add support for showing or hiding completed todo tasks to the *Task list* view.

Reviewed-on: rock-n-code/todos-app#5
Co-authored-by: Javier Cicchelli <javier@rock-n-code.com>
Co-committed-by: Javier Cicchelli <javier@rock-n-code.com>

UnitTests/Tests/Enumerations/TodoGroupTests.swift

@@ -9,6 +9,25 @@ struct TodoGroupTests {
 
     // MARK: Computed tests
 
+    @Test(
+        "canShowCompleted returns correct values",
+        arguments: zip(
+            TodoGroup.allCases,
+            [true, true, true, false]
+        )
+    )
+    func canShowCompleted(
+        for group: TodoGroup,
+        expects expectation: Bool
+    ) {
+        // GIVEN
+        // WHEN
+        let canShowCompleted = group.canShowCompleted
+
+        // THEN
+        #expect(canShowCompleted == expectation)
+    }
+
     @Test(
         "group color match expected values",
         arguments: zip(