refactor(tests): enhance test coverage for move application and piece movement logic

modules/ui/src/test/scala/de/nowchess/ui/utils/RendererAndUnicodeTest.scala

@@ -0,0 +1,38 @@
+package de.nowchess.ui.utils
+
+import de.nowchess.api.board.{Board, Color, File, Piece, PieceType, Rank, Square}
+import org.scalatest.funsuite.AnyFunSuite
+import org.scalatest.matchers.should.Matchers
+
+class RendererAndUnicodeTest extends AnyFunSuite with Matchers:
+
+  private val whiteKing = Piece(Color.White, PieceType.King)
+  private val blackPawn = Piece(Color.Black, PieceType.Pawn)
+
+  test("unicode returns the correct symbol for white king"):
+    whiteKing.unicode shouldBe "\u2654"
+
+  test("unicode returns the correct symbol for black pawn"):
+    blackPawn.unicode shouldBe "\u265F"
+
+  test("render includes board coordinates on top and bottom"):
+    val rendered = Renderer.render(Board(Map.empty))
+    val lines = rendered.trim.split("\\n").toList.map(_.trim)
+
+    lines.head shouldBe "a  b  c  d  e  f  g  h"
+    lines.last shouldBe "a  b  c  d  e  f  g  h"
+
+  test("render includes rank labels from 8 down to 1"):
+    val rendered = Renderer.render(Board(Map.empty))
+
+    rendered should include("8")
+    rendered should include("1")
+
+  test("render places a piece unicode glyph on occupied square"):
+    val board = Board(Map(Square(File.E, Rank.R4) -> Piece(Color.White, PieceType.Queen)))
+    val rendered = Renderer.render(board)
+
+    rendered should include("\u2655")
+    rendered should include("\u001b[")
+
+