Auto merge of #15861 - projektir:make-text-decoration-testable, r=Wafflespeanut

Make text decoration testable and do not serialize initial text-decoration-style

Servo now uses the same name for the text-decoration-line longhand property as Gecko. This was done to enable testing of the text-decoration shorthand.

The text-decoration shorthand has been fixed to not serialize initial text-decoration-style.

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- [x ] `./mach build -d` does not report any errors
- [x ] `./mach test-tidy` does not report any errors
- [x ] These changes fix #15790

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- [x ] There are tests for these changes

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tests/unit/style/properties/serialization.rs

@@ -112,6 +112,47 @@ mod shorthand_serialization {
         }
     }
 
+    mod text {
+        use style::properties::longhands::text_decoration_line as TextDecorationLine;
+        use style::properties::longhands::text_decoration_style::SpecifiedValue as TextDecorationStyle;
+        use super::*;
+
+        #[test]
+        fn text_decoration_should_show_all_properties_when_set() {
+            let mut properties = Vec::new();
+
+            let line = DeclaredValue::Value(TextDecorationLine::OVERLINE);
+            let style = DeclaredValue::Value(TextDecorationStyle::dotted);
+            let color = DeclaredValue::Value(CSSColor {
+                parsed: ComputedColor::RGBA(RGBA::new(128, 0, 128, 255)),
+                authored: None
+            });
+
+            properties.push(PropertyDeclaration::TextDecorationLine(line));
+            properties.push(PropertyDeclaration::TextDecorationStyle(style));
+            properties.push(PropertyDeclaration::TextDecorationColor(color));
+
+            let serialization = shorthand_properties_to_string(properties);
+            assert_eq!(serialization, "text-decoration: overline dotted rgb(128, 0, 128);");
+        }
+
+        #[test]
+        fn text_decoration_should_not_serialize_initial_style_value() {
+            let mut properties = Vec::new();
+
+            let line = DeclaredValue::Value(TextDecorationLine::UNDERLINE);
+            let style = DeclaredValue::Value(TextDecorationStyle::solid);
+            let color = DeclaredValue::Value(CSSColor::currentcolor());
+
+            properties.push(PropertyDeclaration::TextDecorationLine(line));
+            properties.push(PropertyDeclaration::TextDecorationStyle(style));
+            properties.push(PropertyDeclaration::TextDecorationColor(color));
+
+            let serialization = shorthand_properties_to_string(properties);
+            assert_eq!(serialization, "text-decoration: underline;");
+        }
+    }
+
     mod four_sides_shorthands {
         pub use super::*;