diff --git a/.idea/misc.xml b/.idea/misc.xml
index 69ace3f..9d2ecf0 100644
--- a/.idea/misc.xml
+++ b/.idea/misc.xml
@@ -1,4 +1,3 @@
-<?xml version="1.0" encoding="UTF-8"?>
 <project version="4">
   <component name="ProjectRootManager" version="2" languageLevel="JDK_21" default="true" project-jdk-name="openjdk-21" project-jdk-type="JavaSDK">
     <output url="file://$PROJECT_DIR$/out" />
diff --git a/src/ch/epfl/chacun/Area.java b/src/ch/epfl/chacun/Area.java
index ff43219..23b6dbd 100644
--- a/src/ch/epfl/chacun/Area.java
+++ b/src/ch/epfl/chacun/Area.java
@@ -160,11 +160,8 @@ public Set<PlayerColor> majorityOccupants() {
      * @return the new area resulting from the connection
      */
     public Area<Z> connectTo(Area<Z> newArea) {
-        Set<Z> zones = new HashSet<>();
-        zones.addAll(this.zones);
-
-        List<PlayerColor> occupants = new ArrayList<>();
-        occupants.addAll(this.occupants);
+        Set<Z> zones = new HashSet<>(this.zones);
+        List<PlayerColor> occupants = new ArrayList<>(this.occupants);
         // Calculate the new number of open connections
         // The new area will have 2 less open connections, as each area had at least one open connection
         int openConnections = this.openConnections - 2;
diff --git a/src/ch/epfl/chacun/ZonePartition.java b/src/ch/epfl/chacun/ZonePartition.java
index fa5167f..f3bb3ff 100644
--- a/src/ch/epfl/chacun/ZonePartition.java
+++ b/src/ch/epfl/chacun/ZonePartition.java
@@ -144,9 +144,7 @@ public void removeOccupant(Z zone, PlayerColor color) {
          * @throws IllegalArgumentException if the area is not part of the partition
          */
         public void removeAllOccupantsOf(Area<Z> area) {
-            if (!areas.contains(area)) {
-                throw new IllegalArgumentException("The area is not part of the partition.");
-            }
+            Preconditions.checkArgument(areas.contains(area));
             // Create a new area with no occupants
             Area<Z> unoccupiedArea = area.withoutOccupants();
             // Replace the area containing the given zone by the new one in the set of areas
@@ -168,7 +166,15 @@ public void union(Z zone1, Z zone2) {
             Area<Z> area2 = findAreaContainingZone(zone2);
             // If the two zones are not assigned to the same area, connect the two areas
             // Otherwise connect the area to itself
-            area1.connectTo(area1.equals(area2) ? area1 : area2);
+            if(!area1.equals(area2)) {
+                // Remove the two areas from the set of areas and add the new one
+                areas.remove(area1);
+                areas.remove(area2);
+            } else {
+                // Remove the area from the set of areas and add the new one
+                areas.remove(area1);
+            }
+            areas.add(area1.connectTo(area2));
         }
 
         /**
diff --git a/test/ch/epfl/chacun/AreaTest.java b/test/ch/epfl/chacun/AreaTest.java
index 4c238e2..9e8e996 100644
--- a/test/ch/epfl/chacun/AreaTest.java
+++ b/test/ch/epfl/chacun/AreaTest.java
@@ -315,4 +315,35 @@ void withoutOccupantWorks() {
         assertEquals(forestArea2, forestArea1.withoutOccupant(PlayerColor.YELLOW));
     }
 
+    @Test
+    void zoneWithSpecialPowerReturnsNullWhenNoSpecialPower() {
+        Set<Meadow> meadows = new HashSet<>();
+        meadows.add(new Meadow(0, new ArrayList<>(), null));
+        List<PlayerColor> occupants1 = new ArrayList<>(List.of(PlayerColor.YELLOW));
+        Area<Meadow> meadowArea = new Area<>(meadows, occupants1, 3);
+
+        assertNull(meadowArea.zoneWithSpecialPower(SpecialPower.HUNTING_TRAP));
+    }
+
+    @Test
+    void zoneWithSpecialPowerReturnsNullWhenDifferentSpecialPower() {
+        Set<Meadow> meadows = new HashSet<>();
+        meadows.add(new Meadow(0, new ArrayList<>(), SpecialPower.HUNTING_TRAP));
+        List<PlayerColor> occupants1 = new ArrayList<>(List.of(PlayerColor.YELLOW));
+        Area<Meadow> meadowArea = new Area<>(meadows, occupants1, 3);
+
+        assertNull(meadowArea.zoneWithSpecialPower(SpecialPower.LOGBOAT));
+    }
+
+    @Test
+    void zoneWithSpecialPowerWorks() {
+        Set<Meadow> meadows = new HashSet<>();
+        Meadow meadowWithSpecialPower = new Meadow(0, new ArrayList<>(), SpecialPower.HUNTING_TRAP);
+        meadows.add(meadowWithSpecialPower);
+        List<PlayerColor> occupants1 = new ArrayList<>(List.of(PlayerColor.YELLOW));
+        Area<Meadow> meadowArea = new Area<>(meadows, occupants1, 3);
+
+        assertEquals(meadowWithSpecialPower, meadowArea.zoneWithSpecialPower(SpecialPower.HUNTING_TRAP));
+    }
+
 }
diff --git a/test/ch/epfl/chacun/ZonePartitionTest.java b/test/ch/epfl/chacun/ZonePartitionTest.java
new file mode 100644
index 0000000..92443ba
--- /dev/null
+++ b/test/ch/epfl/chacun/ZonePartitionTest.java
@@ -0,0 +1,197 @@
+package ch.epfl.chacun;
+
+import org.junit.jupiter.api.Test;
+
+import java.util.ArrayList;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Set;
+
+import static ch.epfl.chacun.Zone.Forest;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+public class ZonePartitionTest {
+    @Test
+    void areaContainingThrowsOnUnassignedZone() {
+        Set<Forest> forestZones = new HashSet<>();
+        forestZones.add(new Forest(0, Forest.Kind.PLAIN));
+        List<PlayerColor> occupants = new ArrayList<>(List.of(PlayerColor.RED));
+        Area<Forest> forestArea = new Area<>(forestZones, occupants, 3);
+        ZonePartition<Forest> zonePartition = new ZonePartition<>(Set.of(forestArea));
+
+        assertThrows(IllegalArgumentException.class
+                , () -> zonePartition.areaContaining(new Forest(1, Forest.Kind.PLAIN)));
+    }
+
+    @Test
+    void areaContainingWorks() {
+        Set<Forest> forestZones = new HashSet<>();
+        Forest forest = new Forest(0, Forest.Kind.PLAIN);
+        forestZones.add(forest);
+        List<PlayerColor> occupants = new ArrayList<>(List.of(PlayerColor.RED));
+        Area<Forest> forestArea = new Area<>(forestZones, occupants, 3);
+        ZonePartition<Forest> zonePartition = new ZonePartition<>(Set.of(forestArea));
+
+        assertEquals(forestArea, zonePartition.areaContaining(forest));
+    }
+
+    @Test
+    void addSingletonWorks() {
+        Set<Forest> forestZones = new HashSet<>();
+        forestZones.add(new Forest(0, Forest.Kind.PLAIN));
+        List<PlayerColor> occupants = new ArrayList<>(List.of(PlayerColor.RED));
+        Area<Forest> forestArea = new Area<>(forestZones, occupants, 3);
+        ZonePartition<Forest> zonePartition = new ZonePartition<>(Set.of(forestArea));
+        ZonePartition.Builder<Forest> builder = new ZonePartition.Builder<>(zonePartition);
+
+        Set<Forest> newForestZones = new HashSet<>();
+        Forest newForest = new Forest(1, Forest.Kind.WITH_MUSHROOMS);
+        newForestZones.add(newForest);
+        List<PlayerColor> newOccupants = new ArrayList<>();
+        Area<Forest> newForestArea = new Area<>(newForestZones, newOccupants, 1);
+
+        builder.addSingleton(newForest, 1);
+        ZonePartition<Forest> buildedZonePartition = builder.build();
+
+        Set<Area> expectedAreas = new HashSet<>();
+        expectedAreas.add(forestArea);
+        expectedAreas.add(newForestArea);
+
+        assertEquals(expectedAreas, buildedZonePartition.areas());
+    }
+
+    @Test
+    void addInitialOccupantThrowsOnUnAssignedZone() {
+        Set<Forest> forestZones = new HashSet<>();
+        forestZones.add(new Forest(0, Forest.Kind.PLAIN));
+        List<PlayerColor> occupants = new ArrayList<>();
+        Area<Forest> forestArea = new Area<>(forestZones, occupants, 3);
+        ZonePartition<Forest> zonePartition = new ZonePartition<>(Set.of(forestArea));
+        ZonePartition.Builder builder = new ZonePartition.Builder(zonePartition);
+
+        assertThrows(IllegalArgumentException.class
+                , () -> builder.addInitialOccupant(new Forest(1, Forest.Kind.WITH_MENHIR), PlayerColor.BLUE));
+    }
+
+    @Test
+    void addInitialOccupantThrowsOnOccupiedArea() {
+        Set<Forest> forestZones = new HashSet<>();
+        Forest forest = new Forest(0, Forest.Kind.PLAIN);
+        forestZones.add(forest);
+        List<PlayerColor> occupants = new ArrayList<>(List.of(PlayerColor.YELLOW));
+        Area<Forest> forestArea = new Area<>(forestZones, occupants, 3);
+        ZonePartition<Forest> zonePartition = new ZonePartition<>(Set.of(forestArea));
+        ZonePartition.Builder builder = new ZonePartition.Builder(zonePartition);
+
+        assertThrows(IllegalArgumentException.class
+                , () -> builder.addInitialOccupant(forest, PlayerColor.BLUE));
+    }
+
+    @Test
+    void addInitialOccupantWorks() {
+        Set<Forest> forestZones = new HashSet<>();
+        Forest forest = new Forest(0, Forest.Kind.PLAIN);
+        forestZones.add(forest);
+        List<PlayerColor> occupants = new ArrayList<>();
+        Area<Forest> forestArea = new Area<>(forestZones, occupants, 3);
+        ZonePartition<Forest> zonePartition = new ZonePartition<>(Set.of(forestArea));
+        ZonePartition.Builder<Forest> builder = new ZonePartition.Builder<>(zonePartition);
+
+        List<PlayerColor> newOccupants = new ArrayList<>(List.of(PlayerColor.YELLOW));
+        Area<Forest> newForestArea = new Area<>(forestZones, newOccupants, 3);
+
+        builder.addInitialOccupant(forest, PlayerColor.YELLOW);
+        Set<Area> expectedAreas = new HashSet<>();
+        expectedAreas.add(newForestArea);
+
+        assertEquals(expectedAreas, builder.build().areas());
+    }
+
+    @Test
+    void removeOccupantWorks() {
+        Set<Forest> forestZones = new HashSet<>();
+        Forest forest = new Forest(0, Forest.Kind.PLAIN);
+        forestZones.add(forest);
+        List<PlayerColor> occupants = new ArrayList<>(List.of(PlayerColor.YELLOW));
+        Area<Forest> forestArea = new Area<>(forestZones, occupants, 3);
+        ZonePartition<Forest> zonePartition = new ZonePartition<>(Set.of(forestArea));
+        ZonePartition.Builder<Forest> builder = new ZonePartition.Builder<>(zonePartition);
+
+        List<PlayerColor> newOccupants = new ArrayList<>();
+        Area<Forest> newForestArea = new Area<>(forestZones, newOccupants, 3);
+
+        builder.removeOccupant(forest, PlayerColor.YELLOW);
+        Set<Area> expectedAreas = new HashSet<>();
+        expectedAreas.add(newForestArea);
+
+        assertEquals(expectedAreas, builder.build().areas());
+    }
+
+    @Test
+    void removeAllOccupantsOfThrowsOnUnknownArea() {
+        Set<Forest> forestZones = new HashSet<>();
+        Forest forest = new Forest(0, Forest.Kind.PLAIN);
+        forestZones.add(forest);
+        List<PlayerColor> occupants = new ArrayList<>(List.of(PlayerColor.YELLOW));
+        Area<Forest> forestArea = new Area<>(forestZones, occupants, 3);
+
+        ZonePartition<Forest> zonePartition = new ZonePartition<>(Set.of(forestArea));
+        ZonePartition.Builder<Forest> builder = new ZonePartition.Builder<>(zonePartition);
+
+        Forest unknownForest = new Forest(1, Forest.Kind.WITH_MENHIR);
+        Area<Forest> unknownArea = new Area<>(Set.of(unknownForest), occupants, 2);
+
+        assertThrows(IllegalArgumentException.class, () -> builder.removeAllOccupantsOf(unknownArea));
+    }
+
+    @Test
+    void removeAllOccupantsOfWorks() {
+        Set<Forest> forestZones = new HashSet<>();
+        Forest forest = new Forest(0, Forest.Kind.PLAIN);
+        forestZones.add(forest);
+        List<PlayerColor> occupants = new ArrayList<>(List.of(PlayerColor.YELLOW, PlayerColor.GREEN));
+        Area<Forest> forestArea = new Area<>(forestZones, occupants, 3);
+        ZonePartition<Forest> zonePartition = new ZonePartition<>(Set.of(forestArea));
+        ZonePartition.Builder<Forest> builder = new ZonePartition.Builder<>(zonePartition);
+
+        List<PlayerColor> newOccupants = new ArrayList<>();
+        Area<Forest> newForestArea = new Area<>(forestZones, newOccupants, 3);
+
+        builder.removeAllOccupantsOf(forestArea);
+        Set<Area> expectedAreas = new HashSet<>();
+        expectedAreas.add(newForestArea);
+
+        assertEquals(expectedAreas, builder.build().areas());
+    }
+    @Test
+    void unionWorksWithDifferentAreas() {
+        Set<Forest> forestZones1 = new HashSet<>();
+        Forest forest1 = new Forest(0, Forest.Kind.PLAIN);
+        forestZones1.add(forest1);
+        List<PlayerColor> occupants1 = new ArrayList<>(List.of(PlayerColor.YELLOW));
+        Area<Forest> forestArea1 = new Area<>(forestZones1, occupants1, 3);
+
+        Set<Forest> forestZones2 = new HashSet<>();
+        Forest forest2 = new Forest(1, Forest.Kind.WITH_MENHIR);
+        forestZones2.add(forest2);
+        List<PlayerColor> occupants2 = new ArrayList<>(List.of(PlayerColor.RED));
+        Area<Forest> forestArea2 = new Area<>(forestZones2, occupants2, 3);
+
+        ZonePartition<Forest> zonePartition = new ZonePartition<>(Set.of(forestArea1, forestArea2));
+        ZonePartition.Builder<Forest> builder = new ZonePartition.Builder<>(zonePartition);
+
+        Set<Forest> expectedForestZones = new HashSet<>();
+        expectedForestZones.add(forest1);
+        expectedForestZones.add(forest2);
+        List<PlayerColor> expectedOccupants = new ArrayList<>();
+        expectedOccupants.add(PlayerColor.YELLOW);
+        expectedOccupants.add(PlayerColor.RED);
+        Area<Forest> expectedArea = new Area<>(expectedForestZones, expectedOccupants, 4);
+
+        builder.union(forest1, forest2);
+
+        assertEquals(Set.of(expectedArea), builder.build().areas());
+    }
+
+}