Test querySelector on XML documents (#256)

* Improve compatibility with traits' constant usage

* Test query selector methods on XML documents
Closes #174

Author: Greg Bowler

test/phpunit/Helper/Helper.php

@@ -174,13 +174,13 @@ class Helper {
 		<description>light Belgian waffles covered with strawberrys and whipped cream</description>
 		<calories>900</calories>
 	</food>
-	<food>
+	<food special-date="2020-08-30">
 		<name>Berry-Berry Belgian Waffles</name>
 		<price>$8.95</price>
 		<description>light Belgian waffles covered with an assortment of fresh berries and whipped cream</description>
 		<calories>900</calories>
 	</food>
-	<food>
+	<food offer="10%">
 		<name>French Toast</name>
 		<price>$4.50</price>
 		<description>thick slices made from our homemade sourdough bread</description>

test/phpunit/XMLDocumentTest.php

@@ -20,6 +20,31 @@ public function testConstruction() {
 		// test construction from a XMLDocument object, just to be sure
 		$fromXMLDocument = new XMLDocument($fromRawXML);
 		$this->assertInstanceOf(XMLDocument::class, $fromXMLDocument);
+	}
+
+	public function testQuerySelector() {
+		$document = new XMLDocument(Helper::XML);
+		$firstFoodName = $document->querySelector("food name");
+		self::assertEquals("Belgian Waffles", $firstFoodName->nodeValue);
+	}
+
+	public function testQuerySelectorAttribute() {
+		$document = new XMLDocument(Helper::XML);
+		$offerFood = $document->querySelector("food[offer]");
+		self::assertEquals("10%", $offerFood->getAttribute("offer"));
+	}
+
+	public function testQuerySelectorAll() {
+		$document = new XMLDocument(Helper::XML);
+		$totalCalories = 0;
+
+		foreach($document->querySelectorAll("breakfast-menu>food calories") as $caloriesElement) {
+			$totalCalories += (int)$caloriesElement->nodeValue;
+		}
 
+		self::assertEquals(
+			650 + 900 + 900 + 600 + 950,
+			$totalCalories
+		);
 	}
 }