how to write test case for below code : in spark-scala

schema.fields.foreach(f =>
          f.dataType match {
            case arrayType: ArrayType if arrayType.elementType == StringType =>
              // convert array<string> to string
              
              concat_ws(",", col(f.name)).as(f.name)
            case _ => col(f.name)

            }
        )

How can I write test case for above pls help