test: add unit test for clean exit on 'quit' command in Main

modules/core/src/test/scala/de/nowchess/chess/main/MainTest.scala

@@ -0,0 +1,12 @@
+package de.nowchess.chess.main
+
+import de.nowchess.chess.Main
+import java.io.ByteArrayInputStream
+import org.scalatest.funsuite.AnyFunSuite
+import org.scalatest.matchers.should.Matchers
+
+class MainTest extends AnyFunSuite with Matchers:
+
+  test("main exits cleanly when 'quit' is entered"):
+    scala.Console.withIn(ByteArrayInputStream("quit\n".getBytes("UTF-8"))):
+      Main.main(Array.empty)