src/main/java/Shared/LootEntry.java

@@ -0,0 +1,4 @@
+package Shared;
+
+public record LootEntry<T>(T item, int weight) {
+}

src/main/java/Shared/LootTable.java

@@ -1,24 +1,35 @@
 package Shared;
 
 import java.util.ArrayList;
-import java.util.HashMap;
 import java.util.List;
 import java.util.Random;
 
 public class LootTable<T> {
-    private Random random = new Random();
-    private final List<T> items =  new ArrayList<>();
+    private final Random random;
+    private final List<LootEntry<T>> entries =  new ArrayList<>();
 
+    public LootTable() {
+        this.random = new Random();
+    }
     public LootTable(Random random) {
         this.random = random;
     }
 
     public void addEntry(T entry, int weight) {
-        items.add(entry);
+        entries.add(new LootEntry<>(entry,weight));
     }
 
     public T roll() {
-       return items.getFirst();
+        int totalWeight = entries.stream().mapToInt(LootEntry::weight).sum();
+        int roll = random.nextInt(totalWeight);
+        int current = 0;
+        for(LootEntry<T> entry : entries) {
+            current += entry.weight();
+            if (roll < current) {
+                return entry.item();
+            }
+        }
+        return null;
     }
 
 }

src/test/java/LootTableTest.java

@@ -25,10 +25,14 @@ public class LootTableTest {
        assertThat(result, anyOf(equalTo("Stone"), equalTo("Iron")));
     }
 
+    @Test
     void respects_weight_when_rolling() {
-        var mockRandom = mock(Random.class);
-        when(mockRandom.nextInt(anyInt())).thenReturn(94);
-        LootTable<String> loot = new LootTable<>(mockRandom);
+        LootTable<String> loot = new LootTable<>(new Random() {
+            @Override
+            public int nextInt(int bound) {
+                return 94;
+            }
+        });
         loot.addEntry("Stone", 90);
         loot.addEntry("Iron", 10);
         String result = loot.roll();