fix: enforce executable movement state

tests/Unit/Domain/MatchStateTest.php

@@ -7,8 +7,10 @@ namespace BattleForge\Tests\Unit\Domain;
 use BattleForge\Domain\Battlefield;
 use BattleForge\Domain\MatchState;
 use BattleForge\Domain\Position;
+use BattleForge\Domain\Terrain;
 use BattleForge\Domain\UnitState;
 use InvalidArgumentException;
+use PHPUnit\Framework\Attributes\DataProvider;
 use PHPUnit\Framework\TestCase;
 
 final class MatchStateTest extends TestCase
@@ -24,6 +26,67 @@ final class MatchStateTest extends TestCase
         );
     }
 
+    public function testItRejectsAUnitOutsideTheBattlefield(): void
+    {
+        $this->expectException(InvalidArgumentException::class);
+        $this->expectExceptionMessage('Unit alpha-1 is outside the battlefield.');
+
+        new MatchState(
+            new Battlefield(8, 8),
+            [$this->unit('alpha-1', 'alpha', new Position(8, 0))],
+            'alpha',
+        );
+    }
+
+    #[DataProvider('impassableTerrainProvider')]
+    public function testItRejectsALivingUnitOnImpassableTerrain(Terrain $terrain): void
+    {
+        $this->expectException(InvalidArgumentException::class);
+        $this->expectExceptionMessage('Living unit alpha-1 must stand on passable terrain.');
+
+        new MatchState(
+            new Battlefield(8, 8, ['0:0' => $terrain]),
+            [$this->unit('alpha-1', 'alpha')],
+            'alpha',
+        );
+    }
+
+    /**
+     * @return iterable<string, array{Terrain}>
+     */
+    public static function impassableTerrainProvider(): iterable
+    {
+        yield 'water' => [Terrain::Water];
+        yield 'blocking' => [Terrain::Blocking];
+    }
+
+    public function testItRejectsLivingUnitsAtTheSamePosition(): void
+    {
+        $this->expectException(InvalidArgumentException::class);
+        $this->expectExceptionMessage('Living units cannot share position 0:0.');
+
+        new MatchState(
+            new Battlefield(8, 8),
+            [$this->unit('alpha-1', 'alpha'), $this->unit('bravo-1', 'bravo')],
+            'alpha',
+        );
+    }
+
+    public function testItAcceptsLivingAndDefeatedUnitsAtTheSamePosition(): void
+    {
+        $match = new MatchState(
+            new Battlefield(8, 8),
+            [
+                $this->unit('alpha-1', 'alpha'),
+                $this->unit('bravo-1', 'bravo', health: 0),
+            ],
+            'alpha',
+        );
+
+        self::assertSame('0:0', $match->unit('alpha-1')->position->key());
+        self::assertSame('0:0', $match->unit('bravo-1')->position->key());
+    }
+
     public function testItRejectsAnUnknownUnitLookup(): void
     {
         $match = $this->match();
@@ -169,14 +232,21 @@ final class MatchStateTest extends TestCase
     {
         return new MatchState(
             new Battlefield(8, 8),
-            [$this->unit('alpha-1', 'alpha'), $this->unit('bravo-1', 'bravo')],
+            [
+                $this->unit('alpha-1', 'alpha'),
+                $this->unit('bravo-1', 'bravo', new Position(7, 7)),
+            ],
             'alpha',
             actionLog: $actionLog,
         );
     }
 
-    private function unit(string $id, string $teamId): UnitState
-    {
-        return new UnitState($id, $teamId, new Position(0, 0), 10, 10, 4, 2, 4, 2);
+    private function unit(
+        string $id,
+        string $teamId,
+        ?Position $position = null,
+        int $health = 10,
+    ): UnitState {
+        return new UnitState($id, $teamId, $position ?? new Position(0, 0), 10, $health, 4, 2, 4, 2);
     }
 }