add tests for errors
add tests for errors

helensch/ensembl-rest,ens-lgil/ensembl-rest,helensch/ensembl-rest,ens-lgil/ensembl-rest,helensch/ensembl-rest,ens-lgil/ensembl-rest,ens-lgil/ensembl-rest,ens-lgil/ensembl-rest,helensch/ensembl-rest,helensch/ensembl-rest