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/View Models/TaskListViewModelTests.swift

@@ -1,5 +1,6 @@
 import Foundation
 import SwiftData
+import SwiftUI
 import Testing
 
 @testable import Todos
@@ -7,10 +8,73 @@ import Testing
 @Suite("TaskList view model tests")
 struct TaskListViewModelTests {
 
-    // MARK: Computed tests
+    // MARK: Initializers tests
 
     @Test(
-        "navigationTitle returns correct title for each and every group",
+        "properties are set correctly during initialization",
+        arguments: TodoGroup.allCases
+    )
+    func initialization(for group: TodoGroup) {
+        // GIVEN
+        // WHEN
+        let viewModel = TaskListView.ViewModel(group: group)
+
+        // THEN
+        #expect(viewModel.group == group)
+        #expect(viewModel.showCompleted == false)
+    }
+
+    // MARK: Computed property tests
+
+    @Test(
+        "buttonCompleted returns correct values when showCompleted is true",
+        arguments: TodoGroup.allCases, [true, false]
+    )
+    func buttonCompleted(
+        for group: TodoGroup,
+        showCompleted: Bool
+    ) {
+        // GIVEN
+        let viewModel = TaskListView.ViewModel(group: group)
+        
+        viewModel.showCompleted = showCompleted
+
+        // WHEN
+        let (title, icon) = viewModel.buttonCompleted
+
+        // THEN
+        if showCompleted {
+            #expect(title == "view.task-list.label.hide-completed")
+            #expect(icon == "eye.slash")
+        } else {
+            #expect(title == "view.task-list.label.show-completed")
+            #expect(icon == "eye")
+        }
+    }
+
+    @Test(
+        "canShowCompleted returns correct value for each group",
+        arguments: zip(
+            TodoGroup.allCases,
+            [true, true, true, false]
+        )
+    )
+    func canShowCompleted(
+        for group: TodoGroup,
+        expects expectation: Bool
+    ) {
+        // GIVEN
+        let viewModel = TaskListView.ViewModel(group: group)
+
+        // WHEN
+        let canShowCompleted = viewModel.canShowCompleted
+
+        // THEN
+        #expect(canShowCompleted == expectation)
+    }
+
+    @Test(
+        "navigationTitle returns correct view title for each group",
         arguments: TodoGroup.allCases
     )
     func navigationTitle(for group: TodoGroup) {
@@ -24,4 +88,25 @@ struct TaskListViewModelTests {
         #expect(title == group.title)
     }
 
+    // MARK: Method tests
+
+    @Test("toggleCompletedVisbility toggles the showCompleted property")
+    func toggleCompletedVisibility() {
+        // GIVEN
+        let viewModel = TaskListView.ViewModel(group: .today)
+        let initialValue = viewModel.showCompleted
+
+        // WHEN
+        viewModel.toggleCompletedVisibility()
+        let afterFirstToggle = viewModel.showCompleted
+
+        viewModel.toggleCompletedVisibility()
+        let afterSecondToggle = viewModel.showCompleted
+
+        // THEN
+        #expect(initialValue == false)
+        #expect(afterFirstToggle == true)
+        #expect(afterSecondToggle == false)
+    }
+
 }