test(core): add bitboard, fen, and make/unmake tests

tests/Fen.test.scala

@@ -0,0 +1,19 @@
+package gambit
+
+class FenTest extends munit.FunSuite:
+  val cases = List(
+    Fen.startPosition,
+    "r3k2r/p1ppqpb1/bn2pnp1/3PN3/1p2P3/2N2Q1p/PPPBBPPP/R3K2R w KQkq - 0 1",
+    "rnbqkbnr/ppp1pppp/8/3pP3/8/8/PPPP1PPP/RNBQKBNR w KQkq d6 0 3",
+    "8/2p5/3p4/KP5r/1R3p1k/8/4P1P1/8 w - - 0 1",
+    "8/P7/8/8/8/8/8/k6K w - - 5 42"
+  )
+
+  test("fen round trip") {
+    for fen <- cases do assertEquals(Fen.toFen(Fen.parse(fen)), fen)
+  }
+
+  test("startpos hash matches recompute") {
+    val pos = Fen.parse(Fen.startPosition)
+    assertEquals(pos.hash, pos.computeHash())
+  }