add regression check for compiletime.testing.typeChecks

Author: soronpo

tests/run/i12656.scala

@@ -5,4 +5,12 @@ transparent inline def expectCompileError(
   val errors = compiletime.testing.typeCheckErrors(code)
   assert(errors.head.message == expectedMsg, (errors.head.message, expectedMsg))
 
-@main def Test = expectCompileError("""compiletime.error("some error")""", "some error")
+transparent inline def expectTypeCheck(
+  inline code: String,
+) : Boolean = compiletime.testing.typeChecks(code)
+
+@main def Test =
+  assert(!expectTypeCheck("""compiletime.error("some error")"""))
+  assert(expectTypeCheck("""1 + 1"""))
+  expectCompileError("""compiletime.error("some error")""", "some error")
+