test(movegen): add move generation and perft tests

tests/MoveGen.test.scala

@@ -0,0 +1,49 @@
+package gambit
+
+class MoveGenTest extends munit.FunSuite:
+
+  private def legal(fen: String): Vector[Int] =
+    val moves = new MoveList()
+    MoveGen.generateLegal(Fen.parse(fen), moves)
+    (0 until moves.size).map(moves.apply).toVector
+
+  test("en passant generated in matching position") {
+    val moves = legal("rnbqkbnr/ppp1pppp/8/3pP3/8/8/PPPP1PPP/RNBQKBNR w KQkq d6 0 3")
+    val ep = moves.filter(Move.isEnPassant)
+    assertEquals(ep.size, 1)
+    assertEquals(Move.uci(ep.head), "e5d6")
+  }
+
+  test("both castling moves generated when legal") {
+    val moves = legal("r3k2r/8/8/8/8/8/8/R3K2R w KQkq - 0 1")
+    val castles = moves.filter(Move.isCastle).map(Move.uci).toSet
+    assertEquals(castles, Set("e1g1", "e1c1"))
+  }
+
+  test("castling blocked when king passes through check") {
+    val moves = legal("r3k2r/8/8/8/8/8/6q1/R3K2R w KQkq - 0 1")
+    val castles = moves.filter(Move.isCastle).map(Move.uci).toSet
+    assertEquals(castles, Set("e1c1"))
+  }
+
+  test("promotions generated with all four pieces") {
+    val moves = legal("8/P7/8/8/8/8/8/k6K w - - 0 1")
+    val promos = moves.filter(Move.isPromotion).map(Move.uci).toSet
+    assertEquals(promos, Set("a7a8q", "a7a8r", "a7a8b", "a7a8n"))
+  }
+
+  test("pinned knight cannot move") {
+    val moves = legal("4r2k/8/8/8/8/8/4N3/4K3 w - - 0 1")
+    val knightMoves = moves.filter(m => Move.from(m) == Square.make(4, 1))
+    assertEquals(knightMoves.size, 0)
+  }
+
+  test("only check evasions when in check") {
+    val moves = legal("4k3/8/8/8/8/8/8/r3K2R w K - 0 1")
+    assert(moves.nonEmpty)
+    for m <- moves do
+      val pos = Fen.parse("4k3/8/8/8/8/8/8/r3K2R w K - 0 1")
+      val undo = pos.make(m)
+      assert(!pos.isAttacked(pos.kingSquare(Color.White), Color.Black), s"illegal ${Move.uci(m)}")
+      pos.unmake(m, undo)
+  }