How to mock StreamedResponse body?

Question

I was writing test for following code snippet, I am getting nullPointerException for StreamedResponse body. I am not able to mock StreamedResponse body.

I tried mock[StreamedResponse].body returns Source[ByteString("")] But getting Source.type doesn't take parameters error.

streamResponse map {
      case StreamedResponse(response, body) =>
        if (response.status == 200) {
          val contentType = response.headers.get("Content-Type").flatMap(_.headOption).getOrElse("application/pdf")
          response.headers.get("Content-Length") match {
            case Some(Seq(length)) =>
              Ok.sendEntity(HttpEntity.Streamed(body, Some(length.toLong), Some(contentType)))
            case _ =>
              Ok.chunked(body).as(contentType)
          }
        } else {
          Redirect(pdfService.buildEspacenetLink(ucid))
        }
    } 

This is code where I used StreamResponse.

I want to test case _ => Ok.chunked(body).as(contentType) this part of code with some data as response body.