Add failing DatePicker UI tests

MaterialDesignThemes.UITests/WPF/DatePickers/DatePickerTests.cs

@@ -1,5 +1,6 @@
 using System.ComponentModel;
 using System.Globalization;
+using MaterialDesignThemes.UITests.WPF.TextBoxes;
 
 namespace MaterialDesignThemes.UITests.WPF.DatePickers;
 
@@ -112,6 +113,96 @@ public async Task OutlinedDatePicker_RespectsActiveAndInactiveBorderThickness_Wh
 
         recorder.Success();
     }
+
+    [Theory]
+    [InlineData("MaterialDesignFloatingHintDatePicker", null)]
+    [InlineData("MaterialDesignFloatingHintDatePicker", 5)]
+    [InlineData("MaterialDesignFloatingHintDatePicker", 20)]
+    [InlineData("MaterialDesignFilledDatePicker", null)]
+    [InlineData("MaterialDesignFilledDatePicker", 5)]
+    [InlineData("MaterialDesignFilledDatePicker", 20)]
+    [InlineData("MaterialDesignOutlinedDatePicker", null)]
+    [InlineData("MaterialDesignOutlinedDatePicker", 5)]
+    [InlineData("MaterialDesignOutlinedDatePicker", 20)]
+    public async Task DatePicker_WithHintAndHelperText_RespectsPadding(string styleName, int? padding)
+    {
+        await using var recorder = new TestRecorder(App);
+
+        // FIXME: Tolerance needed because TextFieldAssist.TextBoxViewMargin is in play and slightly modifies the hint text placement in certain cases.
+        double tolerance = 1.5;
+
+        string styleAttribute = $"Style=\"{{StaticResource {styleName}}}\"";
+        string paddingAttribute = padding.HasValue ? $"Padding=\"{padding.Value}\"" : string.Empty;
+
+        var datePicker = await LoadXaml<DatePicker>($@"
+<DatePicker {styleAttribute} {paddingAttribute}
+  materialDesign:HintAssist.Hint=""Hint text""
+  materialDesign:HintAssist.HelperText=""Helper text""
+  Width=""200"" VerticalAlignment=""Center"" HorizontalAlignment=""Center"" />
+");
+
+        var contentHost = await datePicker.GetElement<ScrollViewer>("PART_ContentHost");
+        var hint = await datePicker.GetElement<SmartHint>("Hint");
+        var helperText = await datePicker.GetElement<TextBlock>("HelperTextTextBlock");
+
+        Rect? contentHostCoordinates = await contentHost.GetCoordinates();
+        Rect? hintCoordinates = await hint.GetCoordinates();
+        Rect? helperTextCoordinates = await helperText.GetCoordinates();
+
+        Assert.InRange(Math.Abs(contentHostCoordinates.Value.Left - hintCoordinates.Value.Left), 0, tolerance);
+        Assert.InRange(Math.Abs(contentHostCoordinates.Value.Left - helperTextCoordinates.Value.Left), 0, tolerance);
+
+        recorder.Success();
+    }
+
+    [Theory]
+    [InlineData("MaterialDesignFloatingHintDatePicker", null)]
+    [InlineData("MaterialDesignFloatingHintDatePicker", 5)]
+    [InlineData("MaterialDesignFloatingHintDatePicker", 20)]
+    [InlineData("MaterialDesignFilledDatePicker", null)]
+    [InlineData("MaterialDesignFilledDatePicker", 5)]
+    [InlineData("MaterialDesignFilledDatePicker", 20)]
+    [InlineData("MaterialDesignOutlinedDatePicker", null)]
+    [InlineData("MaterialDesignOutlinedDatePicker", 5)]
+    [InlineData("MaterialDesignOutlinedDatePicker", 20)]
+    public async Task DatePicker_WithHintAndValidationError_RespectsPadding(string styleName, int? padding)
+    {
+        await using var recorder = new TestRecorder(App);
+
+        // FIXME: Tolerance needed because TextFieldAssist.TextBoxViewMargin is in play and slightly modifies the hint text placement in certain cases.
+        double tolerance = 1.5;
+
+        string styleAttribute = $"Style=\"{{StaticResource {styleName}}}\"";
+        string paddingAttribute = padding.HasValue ? $"Padding=\"{padding.Value}\"" : string.Empty;
+
+        var datePicker = await LoadXaml<DatePicker>($@"
+<DatePicker {styleAttribute} {paddingAttribute}
+  materialDesign:HintAssist.Hint=""Hint text""
+  materialDesign:HintAssist.HelperText=""Helper text""
+  Width=""200"" VerticalAlignment=""Center"" HorizontalAlignment=""Center"">
+  <DatePicker.Text>
+    <Binding RelativeSource=""{{RelativeSource Self}}"" Path=""Tag"" UpdateSourceTrigger=""PropertyChanged"">
+      <Binding.ValidationRules>
+        <local:NotEmptyValidationRule ValidatesOnTargetUpdated=""True""/>
+      </Binding.ValidationRules>
+    </Binding>
+  </DatePicker.Text>
+</DatePicker>
+", ("local", typeof(NotEmptyValidationRule)));
+
+        var contentHost = await datePicker.GetElement<ScrollViewer>("PART_ContentHost");
+        var hint = await datePicker.GetElement<SmartHint>("Hint");
+        var errorViewer = await datePicker.GetElement<Border>("DefaultErrorViewer");
+
+        Rect? contentHostCoordinates = await contentHost.GetCoordinates();
+        Rect? hintCoordinates = await hint.GetCoordinates();
+        Rect? errorViewerCoordinates = await errorViewer.GetCoordinates();
+
+        Assert.InRange(Math.Abs(contentHostCoordinates.Value.Left - hintCoordinates.Value.Left), 0, tolerance);
+        Assert.InRange(Math.Abs(contentHostCoordinates.Value.Left - errorViewerCoordinates.Value.Left), 0, tolerance);
+
+        recorder.Success();
+    }
 }
 
 public class FutureDateValidationRule : ValidationRule

MaterialDesignThemes.Wpf/Themes/MaterialDesignTheme.DatePicker.xaml

@@ -212,7 +212,7 @@
                            CornerRadius="{TemplateBinding wpf:TextFieldAssist.UnderlineCornerRadius}"
                            Visibility="{TemplateBinding wpf:TextFieldAssist.DecorationVisibility}" />
             <Canvas x:Name="HelperTextWrapper" VerticalAlignment="Bottom">
-              <TextBlock Canvas.Top="2"
+              <TextBlock x:Name="HelperTextTextBlock" Canvas.Top="2"
                          MaxWidth="{Binding ActualWidth, ElementName=border}"
                          FontSize="{TemplateBinding wpf:HintAssist.HelperTextFontSize}"
                          Opacity="{TemplateBinding wpf:HintAssist.HintOpacity}"