test_get_ppi_enrichment <- function() {

  string_db <- STRINGdb$new( version="12.0", species=9606, score_threshold=400)
  data(diff_exp_example1)
  example = string_db$map( diff_exp_example1, "gene", removeUnmappedRows = TRUE )  
  hits = example$STRING_id[1:20]
  string_db$set_background(hits) 
  ppi_enrichment = string_db$get_ppi_enrichment( hits )
  checkTrue( ppi_enrichment$enrichment >= 0.2 )

}
