Fix nullability errors in UI tests

tests/MaterialDesignThemes.UITests/WPF/DialogHosts/DialogHostTests.cs

@@ -235,19 +235,19 @@ public async Task DialogBackgroundShouldInheritThemeBackground(BaseTheme dialogT
         await Wait.For(async () =>
         {
             Color? foreground1 = await textBlock1.GetForegroundColor();
-            await Assert.That(foreground1).IsNotNull();
+            Color foreground1Value = await Assert.That(foreground1).IsNotNull();
             await AssertContrastRatio(
-                foreground1.Value,
+                foreground1Value,
                 await textBlock1.GetEffectiveBackground(),
                 MinimumContrastSmallText);
         });
 
         await Wait.For(async () =>
         {
             Color? foreground2 = await textBlock2.GetForegroundColor();
-            await Assert.That(foreground2).IsNotNull();
+            Color foreground2Value = await Assert.That(foreground2).IsNotNull();
             await AssertContrastRatio(
-                foreground2.Value,
+                foreground2Value,
                 await textBlock2.GetEffectiveBackground(),
                 MinimumContrastSmallText);
         });

tests/MaterialDesignThemes.UITests/WPF/TabControls/TabControlTests.cs

@@ -35,12 +35,12 @@ public async Task OnLoad_ThemeBrushesSet()
         Color? selectedTabUnderline = await selectedTabBorder.GetBorderBrushColor();
 
         //Assert
-        await Assert.That(foreground).IsNotNull();
-        await Assert.That(background).IsNotNull();
+        Color foregroundValue = await Assert.That(foreground).IsNotNull();
+        Color backgroundValue = await Assert.That(background).IsNotNull();
 
-        await MaterialDesignSpec.AssertContrastRatio(foreground.Value, background.Value, MaterialDesignSpec.MinimumContrastSmallText);
+        await MaterialDesignSpec.AssertContrastRatio(foregroundValue, backgroundValue, MaterialDesignSpec.MinimumContrastSmallText);
 
-        await Assert.That(selectedTabUnderline).IsEqualTo(foreground);
+        await Assert.That(selectedTabUnderline).IsEqualTo(foregroundValue);
 
         recorder.Success();
     }

tests/MaterialDesignThemes.UITests/WPF/Theme/ColorAdjustTests.cs

@@ -47,11 +47,13 @@ async Task AssertContrastRatio()
 
             Color? smallTextForeground = await smallText.GetForegroundColor();
             Color smallTextBackground = await smallText.GetEffectiveBackground();
+            Color largeTextForegroundValue = await Assert.That(largeTextForeground).IsNotNull();
+            Color smallTextForegroundValue = await Assert.That(smallTextForeground).IsNotNull();
 
-            double largeContrastRatio = ColorAssist.ContrastRatio(largeTextForeground.Value, largeTextBackground);
+            double largeContrastRatio = ColorAssist.ContrastRatio(largeTextForegroundValue, largeTextBackground);
             await Assert.That(largeContrastRatio).IsGreaterThanOrEqualTo(MaterialDesignSpec.MinimumContrastLargeText - tolerance)
                 .Because($"Large font contrast ratio '{largeContrastRatio}' does not meet material design spec {MaterialDesignSpec.MinimumContrastLargeText}");
-            double smallContrastRatio = ColorAssist.ContrastRatio(smallTextForeground.Value, smallTextBackground);
+            double smallContrastRatio = ColorAssist.ContrastRatio(smallTextForegroundValue, smallTextBackground);
             await Assert.That(smallContrastRatio).IsGreaterThanOrEqualTo(MaterialDesignSpec.MinimumContrastSmallText - tolerance).Because($"Small font contrast ratio '{smallContrastRatio}' does not meet material design spec {MaterialDesignSpec.MinimumContrastSmallText}");
         }
     }