test: strengthen battlefield boundary coverage

tests/Unit/Domain/BattlefieldTest.php

@@ -19,6 +19,22 @@ final class BattlefieldTest extends TestCase
         new Battlefield(7, 16);
     }
 
+    public function testItAcceptsMinimumAndMaximumDimensions(): void
+    {
+        $minimum = new Battlefield(8, 8);
+        $maximum = new Battlefield(16, 16);
+
+        self::assertSame([8, 8], [$minimum->width, $minimum->height]);
+        self::assertSame([16, 16], [$maximum->width, $maximum->height]);
+    }
+
+    public function testItRejectsDimensionsAboveTheSupportedRange(): void
+    {
+        $this->expectException(InvalidArgumentException::class);
+
+        new Battlefield(16, 17);
+    }
+
     public function testItRejectsNonCanonicalTerrainCoordinates(): void
     {
         $this->expectException(InvalidArgumentException::class);
@@ -37,9 +53,8 @@ final class BattlefieldTest extends TestCase
     {
         $this->expectException(InvalidArgumentException::class);
 
-        $terrain = ['0:0' => 'forest'];
-
-        new Battlefield(8, 8, $terrain);
+        // @phpstan-ignore argument.type
+        new Battlefield(8, 8, ['0:0' => 'forest']);
     }
 
     public function testReachableRejectsAStartOutsideTheBattlefield(): void
@@ -90,4 +105,17 @@ final class BattlefieldTest extends TestCase
             '0:1' => 2,
         ], $reachable);
     }
+
+    public function testReachableReplacesAHighCostRouteWithALowerCostDetour(): void
+    {
+        $battlefield = new Battlefield(8, 8, [
+            '1:0' => Terrain::Forest,
+            '2:0' => Terrain::Forest,
+            '3:0' => Terrain::Forest,
+        ]);
+
+        $reachable = $battlefield->reachable(new Position(0, 0), 7, []);
+
+        self::assertSame(6, $reachable['4:0']);
+    }
 }