src/main/java/Monster/Troll.java

@@ -101,6 +101,9 @@ public class Troll extends Monster implements CanMove, CanAttack {
         if (playerIsAtPosition(destination, world)) {
             return false;
         }
+        if (tileHasWrongHabitat(position, world)) {
+            return false;
+        }
 
         position = destination;
         updateDestinations(position, world);
@@ -159,4 +162,8 @@ public class Troll extends Monster implements CanMove, CanAttack {
     private boolean attackIsNotInArsenal(Attacks attack) {
         return !ATTACKS.contains(attack);
     }
+
+    private boolean tileHasWrongHabitat(Position position, World world) {
+        return !HABITAT.contains(world.getTileAtPosition(position).getBiome());
+    }
 }

src/test/java/MonsterTest.java

@@ -195,11 +195,14 @@ public class MonsterTest {
 
     @Test
     void troll_wont_move_to_tile_with_wrong_biome() {
-        Position destination = new Position(1, 3);
         when(mockTile.getBiome()).thenReturn(Biomes.COAST);
-        when(mockWorld.getTileAtPosition(destination)).thenReturn(mockTile);
+        Position destination = new Position(1, 3);
 
-        assertThat(false, equalTo(defaultTroll.moveTo(destination, mockWorld)));
+        worldGenerator.randomWorldGeneration();
+        World world = worldGenerator.getWorld();
+        world.addTile(mockTile, destination);
+
+        assertThat(defaultTroll.moveTo(destination, world), equalTo(false));
     }
 
 }