added tests

Kotlin/build.gradle.kts

@@ -14,6 +14,7 @@ repositories {
 dependencies {
 	implementation(kotlin("stdlib"))
 	testImplementation("org.junit.jupiter:junit-jupiter:5.8.2")
+	testImplementation("org.assertj:assertj-core:3.21.0")
 }
 
 tasks.test {

Kotlin/src/test/kotlin/com/gildedrose/GildedRoseTest.kt

@@ -1,17 +1,100 @@
 package com.gildedrose
 
-import org.junit.jupiter.api.Assertions.assertEquals
+import org.assertj.core.api.Assertions.assertThat
 import org.junit.jupiter.api.Test
 
 internal class GildedRoseTest {
 
     @Test
-    fun foo() {
-        val items = arrayOf<Item>(Item("foo", 0, 0))
+    fun agedBrie_increasesInQuality() {
+        val item = Item("Aged Brie", 2, 2)
+        val app = GildedRose(arrayOf(item))
+        app.updateQuality()
+        assertThat(item.quality).isEqualTo(3)
+    }
+
+    @Test
+    fun agedBrie_increasesInQualityBy2WhenSellInPasses() {
+        val item = Item("Aged Brie", -2, 2)
+        val app = GildedRose(arrayOf(item))
+        app.updateQuality()
+        assertThat(item.quality).isEqualTo(4)
+    }
+
+    @Test
+    fun itemsExceptSulfurasQualityNeverNegative() {
+        val items = arrayOf(
+            Item("Aged Brie", 2, 0),
+            Item("Backstage passes to a TAFKAL80ETC concert", 1, 0),
+        )
         val app = GildedRose(items)
         app.updateQuality()
-        assertEquals("fixme", app.items[0].name)
+        items.forEach { item ->
+            assertThat(item.quality).isGreaterThanOrEqualTo(0)
+        }
+    }
 
+    @Test
+    fun itemsExceptSulfurasQualityNeverGreaterThan50() {
+        val items = arrayOf(
+            Item("Aged Brie", 2, 50),
+            Item("Backstage passes to a TAFKAL80ETC concert", 1, 50),
+        )
+        val app = GildedRose(items)
+        app.updateQuality()
+        items.forEach { item ->
+            assertThat(item.quality).isLessThanOrEqualTo(50)
+        }
+    }
+
+    @Test
+    fun decreaseValueOfAnItemByTheEndOfADay() {
+        val item = Item("Elixir of the Mongoose", 5, 7)
+        val app = GildedRose(arrayOf(item))
+        app.updateQuality()
+        assertThat(item.quality).isEqualTo(6)
+        assertThat(item.sellIn).isEqualTo(4)
+    }
+
+    @Test
+    fun sulfurasNeverDecreaseQuality() {
+        val item = Item("Sulfuras, Hand of Ragnaros", 5, 80)
+        val app = GildedRose(arrayOf(item))
+        app.updateQuality()
+        assertThat(item.quality).isEqualTo(80)
+    }
+
+    @Test
+    fun backStagePassesIncreasesQualityByTwoInside10Days() {
+        val item = Item("Backstage passes to a TAFKAL80ETC concert", 10, 4)
+        val app = GildedRose(arrayOf(item))
+        app.updateQuality()
+        assertThat(item.quality).isEqualTo(6)
+    }
+
+    @Test
+    fun backStagePassesIncreasesQualityBy3Inside5Days() {
+        val item = Item("Backstage passes to a TAFKAL80ETC concert", 5, 4)
+        val app = GildedRose(arrayOf(item))
+        app.updateQuality()
+        assertThat(item.quality).isEqualTo(7)
+    }
+
+    @Test
+    fun backStagePassesQualityGoesToZeroWhenSellInExpires() {
+        val item = Item("Backstage passes to a TAFKAL80ETC concert", 0, 4)
+        val app = GildedRose(arrayOf(item))
+        app.updateQuality()
+        assertThat(item.quality).isEqualTo(0)
+        assertThat(item.sellIn).isEqualTo(-1)
+    }
+
+    @Test
+    fun decreaseQualityOfAnItemByTwoWhenSellDatePasses() {
+        val item = Item("Elixir of the Mongoose", -1, 7)
+        val app = GildedRose(arrayOf(item))
+        app.updateQuality()
+        assertThat(item.quality).isEqualTo(5)
     }
 
 }