feat(scala): m01–m06 port with shared fixtures

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

scala/test/M04Spawn.test.scala

@@ -0,0 +1,52 @@
+package snake
+
+import Fixtures.*
+
+class M04SpawnSuite extends munit.FunSuite:
+  cases("m04-free-cells").foreach { c =>
+    test(s"freeCells: ${c("name").str}") {
+      assertEquals(Spawn.freeCells(gameState(c("args")(0))), list(c("expected"))(point))
+    }
+  }
+
+  cases("m04-spawn").foreach { c =>
+    test(s"spawnApple: ${c("name").str}") {
+      assertEquals(Spawn.spawnApple(gameState(c("args")(0))), gameState(c("expected")))
+    }
+  }
+
+  cases("m04-new-game").foreach { c =>
+    test(s"newGame: ${c("name").str}") {
+      assertEquals(Spawn.newGame(c("args")(0).num.toLong), gameState(c("expected")))
+    }
+  }
+
+  cases("m04-tick").foreach { c =>
+    test(s"tick: ${c("name").str}") {
+      assertEquals(Spawn.tick(gameState(c("args")(0))), gameState(c("expected")))
+    }
+  }
+
+  // 3x2 board, one-cell snake, about to eat the apple at (1,0)
+  private val eating = GameState(3, 2, List(Point(0, 0)), Direction.Right, Direction.Right,
+    Some(Point(1, 0)), 0L, 0, Status.Playing, 0)
+
+  test("tick: eating the apple spawns a new one in the same step") {
+    // snake becomes (1,0),(0,0); free cells are (2,0),(0,1),(1,1),(2,1); seed 0 draws 1144304738 % 4 = 2 -> (1,1)
+    assertEquals(
+      Spawn.tick(eating),
+      eating.copy(snake = List(Point(1, 0), Point(0, 0)), apple = Some(Point(1, 1)), score = 1, seed = 1831565813L)
+    )
+  }
+
+  test("tick is spawnApple after advance") {
+    assertEquals(Spawn.tick(eating), Spawn.spawnApple(Rules.advance(eating)))
+  }
+
+  test("tick leaves the seed alone when no apple needs spawning") {
+    assertEquals(Spawn.tick(eating.copy(apple = Some(Point(2, 1)))).seed, 0L)
+  }
+
+  test("newGame is reproducible: same seed, same game") {
+    assertEquals(Spawn.newGame(42L), Spawn.newGame(42L))
+  }