Question

I am testing a parser I have written in Scala using ScalaTest. The parser handles one file at a time and it has a singleton object like following:

class Parser{...}
object Resolver {...}

The test case I have written is somewhat like this

   describe("Syntax:") {
    val dir = new File("tests\\syntax");
    val files = dir.listFiles.filter(
                    f => """.*\.chalice$""".r.findFirstIn(f.getName).isDefined);

    for(inputFile <- files) {
      val parser = new Parser();
      val c = Resolver.getClass.getConstructor();
      c.setAccessible(true);
      c.newInstance();

      val iserror = errortest(inputFile)
      val result = invokeparser(parser,inputFile.getAbsolutePath) //local method
      it(inputFile.getName + (if (iserror)" ERR" else " NOERR") ){
      if (!iserror) result should be (ResolverSuccess()) 
        else if(result.isInstanceOf[ResolverError]) assert(true)
      }
    }
  }

Now at each iteration the side effects of previous iterations inside the singleton object Resolver are not cleaned up.

Is there any way to specify to scalatest module to re-initialize the singleton objects?

Update: Using Daniel’s suggestion, I have updated the code, also added more details.

Update: Apparently it is the Parser which is doing something fishy. At subsequent calls it doesn’t discard the previous AST. strange. since this is off topic, I would dig more and probably use a separate thread for the discussion, thanks all for answering

Final Update: The issue was with a singleton object other than Resolver, it was in some other file so I had somehow missed it. I was able to solve this using Daniel Spiewak’s reply. It is dirty way to do things but its also the only thing, given my circumstances and also given the fact I am writing a test code, which is not going into production use.

Answer 1

According to the language spec, no, there is no way to recreate singleton objects. However, it is possible to reflectively invoke the constructor of a singleton, which overwrites the internal MODULE$ field which contains the actual singleton value:

object Test

Test.hashCode    // => e.g. 779942019

val c = Test.getClass.getConstructor()
c.setAccessible(true)
c.newInstance()

Test.hashCode    // => e.g. 1806030550

Now that I’ve shared the evil secret with you, let me caution you never, ever to do this. I would try very very hard to adjust the code, rather than playing sneaky tricks like this one. However, if things are as you say, and you really do have no other option, this is at least something.