Added base rules

swift/Tests/GildedRoseTests/BaseRules.swift

@@ -0,0 +1,45 @@
+//
+//  BaseRules.swift
+//  GildedRose
+//
+//  Created by Lucas van Dongen on 23/11/2020.
+//
+
+@testable import GildedRose
+import XCTest
+
+class BaseRules: XCTestCase {
+    private let testItem = Item(name: "Test Item", sellIn: 3, quality: 5)
+
+    //- All items have a SellIn value which denotes the number of days we have to sell the item
+    func testSellInTest() {
+        let itemMirror = Mirror(reflecting: testItem)
+        let hasSellIn = itemMirror.children.contains { (child: (label: String?, _: Any)) -> Bool in
+            child.label == "sellIn"
+        }
+
+        XCTAssertTrue(hasSellIn, "`sellIn` was not a member of `Item`")
+    }
+
+    //- All items have a Quality value which denotes how valuable the item is
+    func testQualityValue() {
+        let itemMirror = Mirror(reflecting: testItem)
+        let hasSellIn = itemMirror.children.contains { (child: (label: String?, _: Any)) -> Bool in
+            child.label == "quality"
+        }
+
+        XCTAssertTrue(hasSellIn, "`quality` was not a member of `Item`")
+    }
+
+    //- At the end of each day our system lowers both values for every item
+    func testLowerValueEveryItem() {
+        let initialSellIn = testItem.sellIn
+        let initialQuality = testItem.quality
+
+        let system = GildedRose(items: [testItem])
+        system.updateQuality()
+
+        XCTAssertLessThan(system.items.first!.sellIn, initialSellIn)
+        XCTAssertLessThan(system.items.first!.quality, initialQuality)
+    }
+}