Add a test.

game-app/game-core/src/main/java/games/strategy/triplea/delegate/battle/casualty/CasualtySelector.java

@@ -125,6 +125,7 @@ public static CasualtyDetails selectCasualties(
 
     final CasualtyDetails casualtyDetails =
         hitsRemaining >= totalHitpoints
+                || sortedTargetsToPickFrom.size() == 1
                 || allTargetsOneTypeOneHitPoint(
                     sortedTargetsToPickFrom,
                     dependents,

game-app/game-core/src/test/java/games/strategy/triplea/delegate/GameDataTestUtil.java

@@ -422,7 +422,7 @@ public static void move(final Collection<Unit> units, final Route route) {
     }
   }
 
-  static void assertMoveError(final Collection<Unit> units, final Route route) {
+  public static void assertMoveError(final Collection<Unit> units, final Route route) {
     Preconditions.checkArgument(!units.isEmpty());
     final String error = moveDelegate(route.getStart().getData()).move(units, route);
     if (error == null) {

game-app/game-core/src/test/java/games/strategy/triplea/delegate/battle/MustFightBattleTest.java

@@ -11,6 +11,7 @@
 import static games.strategy.triplea.delegate.GameDataTestUtil.chinese;
 import static games.strategy.triplea.delegate.GameDataTestUtil.fighter;
 import static games.strategy.triplea.delegate.GameDataTestUtil.french;
+import static games.strategy.triplea.delegate.GameDataTestUtil.germanBattleship;
 import static games.strategy.triplea.delegate.GameDataTestUtil.germans;
 import static games.strategy.triplea.delegate.GameDataTestUtil.infantry;
 import static games.strategy.triplea.delegate.GameDataTestUtil.japan;
@@ -20,6 +21,7 @@
 import static games.strategy.triplea.delegate.GameDataTestUtil.removeFrom;
 import static games.strategy.triplea.delegate.GameDataTestUtil.territory;
 import static games.strategy.triplea.delegate.GameDataTestUtil.transport;
+import static games.strategy.triplea.delegate.GameDataTestUtil.unitType;
 import static games.strategy.triplea.delegate.MockDelegateBridge.advanceToStep;
 import static games.strategy.triplea.delegate.MockDelegateBridge.newDelegateBridge;
 import static games.strategy.triplea.delegate.MockDelegateBridge.thenGetRandomShouldHaveBeenCalled;
@@ -32,6 +34,7 @@
 import static org.hamcrest.Matchers.in;
 import static org.hamcrest.core.Is.is;
 import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertNotNull;
 import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.ArgumentMatchers.anyString;
@@ -51,13 +54,15 @@
 import games.strategy.triplea.attachments.UnitSupportAttachment;
 import games.strategy.triplea.delegate.AbstractMoveDelegate;
 import games.strategy.triplea.delegate.GameDataTestUtil;
+import games.strategy.triplea.delegate.Matches;
 import games.strategy.triplea.delegate.MoveDelegate;
 import games.strategy.triplea.settings.AbstractClientSettingTestCase;
 import games.strategy.triplea.xml.TestMapGameData;
 import java.util.Collection;
 import java.util.List;
 import java.util.Set;
 import org.junit.jupiter.api.Test;
+import org.triplea.java.collections.CollectionUtils;
 
 class MustFightBattleTest extends AbstractClientSettingTestCase {
   @Test
@@ -222,7 +227,7 @@ void testStepNamesChangeDuringCombat() {
   }
 
   @Test
-  void testAlliedCarriedPlanesTransportedByIsResetWhenCancelingBattle() throws Exception {
+  void testAlliedCarriedPlanesTransportedByIsResetWhenCancelingBattle() {
     // Note: Test uses germans, british and france since other countries aren't at war on t1.
     final GameData gameData = TestMapGameData.GLOBAL1940.getGameData();
 
@@ -259,6 +264,42 @@ void testAlliedCarriedPlanesTransportedByIsResetWhenCancelingBattle() throws Exc
     assertThat(fighters.get(1).getTransportedBy(), is(nullValue()));
   }
 
+  @Test
+  void testCantMoveAfterHitTransform() {
+    final GameData gameData = TestMapGameData.TWW.getGameData();
+    final Territory sz23 = territory("23 Sea Zone", gameData);
+    removeFrom(sz23, sz23.getUnits());
+    final Territory sz25 = territory("25 Sea Zone", gameData);
+    removeFrom(sz25, sz25.getUnits());
+
+    addTo(sz25, germanBattleship(gameData).create(1, GameDataTestUtil.germany(gameData)));
+    addTo(sz23, unitType("americanDestroyer", gameData).create(1, GameDataTestUtil.usa(gameData)));
+
+    final Collection<Unit> attackers = List.copyOf(sz25.getUnits());
+    final IDelegateBridge bridge =
+        performCombatMove(GameDataTestUtil.germany(gameData), attackers, new Route(sz25, sz23));
+
+    final IBattle battle = AbstractMoveDelegate.getBattleTracker(gameData).getPendingBattle(sz23);
+    assertNotNull(battle);
+    // Attacking battleship rolls a die with a hit, killing the destroyer.
+    // Defenders should roll a die with a hit, damaging the battleship.
+    whenGetRandom(bridge).thenAnswer(withDiceValues(1)).thenAnswer(withDiceValues(1));
+    battle.fight(bridge);
+    // The unit left should be the damaged german battleship.
+    assertEquals(1, sz23.getUnits().size());
+    final Unit unit = CollectionUtils.getAny(sz23.getUnits());
+    assertEquals("germanBattleship-damaged", unit.getType().getName());
+    // And it should have no movement left.
+    assertFalse(Matches.unitHasMovementLeft().test(unit));
+
+    // And just to double check, we can't move it.
+    advanceToStep(bridge, "NonCombatMove");
+    MoveDelegate moveDelegate = GameDataTestUtil.moveDelegate(gameData);
+    moveDelegate.setDelegateBridgeAndPlayer(bridge);
+    moveDelegate.start();
+    GameDataTestUtil.assertMoveError(sz23.getUnits(), new Route(sz23, sz25));
+  }
+
   private static <T> void setPropertyValue(GameData gameData, String propertyName, T value) {
     IEditableProperty<T> property =
         (IEditableProperty<T>)

game-app/game-core/src/test/resources/Total_World_War_Dec1941.xml

@@ -1975,6 +1975,7 @@
     <unit name="germanAdvancedRocket"/>
     <unit name="germanTransport"/>
     <unit name="germanBattleship"/>
+    <unit name="germanBattleship-damaged"/>
     <unit name="germanHull"/>
     <unit name="germanCarrier"/>
     <unit name="germanSubmarine"/>
@@ -8049,6 +8050,18 @@
       <option name="requiresUnits" value="germanDocks:germanFactory"/>
       <option name="consumesUnits" value="1:germanHull"/>
       <option name="tuv" value="25"/>
+      <option name="whenHitPointsDamagedChangesInto" value="1:true:germanBattleship-damaged"/>
+    </attachment>
+    <attachment name="unitAttachment" attachTo="germanBattleship-damaged" javaClass="UnitAttachment" type="unitType">
+      <option name="movement" value="1"/>
+      <option name="attack" value="6"/>
+      <option name="defense" value="5"/>
+      <option name="canBombard" value="true"/>
+      <option name="isSea" value="true"/>
+      <option name="hitPoints" value="2"/>
+      <option name="bombard" value="5"/>
+      <option name="whenHitPointsRepairedChangesInto" value="0:true:germanBattleship"/>
+      <option name="tuv" value="17"/>
     </attachment>
     <attachment name="unitAttachment" attachTo="germanHull" javaClass="games.strategy.triplea.attachments.UnitAttachment" type="unitType">
       <option name="movement" value="0"/>