test:WIP add tests. Change decade context end date.

tests/Test.Ursa/DateTimePickerTests/CalendarDayButtonTests.cs

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+using Avalonia.Input;
+using Irihi.Avalonia.Shared.Common;
+using CalendarDayButton = Ursa.Controls.CalendarDayButton;
+
+namespace Test.Ursa.DateTimePicker;
+
+public class CalendarDayButtonTests
+{
+    [Fact]
+    public void IsToday_SetsPseudoClass()
+    {
+        var button = new CalendarDayButton();
+        button.IsToday = true;
+        Assert.Contains(CalendarDayButton.PC_Today, button.Classes);
+    }
+
+    [Fact]
+    public void IsStartDate_SetsPseudoClass()
+    {
+        var button = new CalendarDayButton();
+        button.IsStartDate = true;
+        Assert.Contains(CalendarDayButton.PC_StartDate, button.Classes);
+    }
+
+    [Fact]
+    public void IsEndDate_SetsPseudoClass()
+    {
+        var button = new CalendarDayButton();
+        button.IsEndDate = true;
+        Assert.Contains(CalendarDayButton.PC_EndDate, button.Classes);
+    }
+
+    [Fact]
+    public void IsPreviewStartDate_SetsPseudoClass()
+    {
+        var button = new CalendarDayButton();
+        button.IsPreviewStartDate = true;
+        Assert.Contains(CalendarDayButton.PC_PreviewStartDate, button.Classes);
+    }
+
+    [Fact]
+    public void IsPreviewEndDate_SetsPseudoClass()
+    {
+        var button = new CalendarDayButton();
+        button.IsPreviewEndDate = true;
+        Assert.Contains(CalendarDayButton.PC_PreviewEndDate, button.Classes);
+    }
+
+    [Fact]
+    public void IsInRange_SetsPseudoClass()
+    {
+        var button = new CalendarDayButton();
+        button.IsInRange = true;
+        Assert.Contains(CalendarDayButton.PC_InRange, button.Classes);
+    }
+
+    [Fact]
+    public void IsSelected_SetsPseudoClass()
+    {
+        var button = new CalendarDayButton();
+        button.IsSelected = true;
+        Assert.Contains(PseudoClassName.PC_Selected, button.Classes);
+    }
+
+    [Fact]
+    public void IsBlackout_SetsPseudoClass()
+    {
+        var button = new CalendarDayButton();
+        button.IsBlackout = true;
+        Assert.Contains(CalendarDayButton.PC_Blackout, button.Classes);
+    }
+
+    [Fact]
+    public void IsNotCurrentMonth_SetsPseudoClass()
+    {
+        var button = new CalendarDayButton();
+        button.IsNotCurrentMonth = true;
+        Assert.Contains(CalendarDayButton.PC_NotCurrentMonth, button.Classes);
+    }
+
+    [Fact]
+    public void ResetSelection_ClearsPseudoClasses()
+    {
+        var button = new CalendarDayButton();
+        button.IsSelected = true;
+        button.IsStartDate = true;
+        button.ResetSelection();
+        Assert.DoesNotContain(PseudoClassName.PC_Selected, button.Classes);
+        Assert.DoesNotContain(CalendarDayButton.PC_StartDate, button.Classes);
+    }
+}