At the Radio Science laboratory of the University of Bologna in Forlì a dedicated GNSS data analysis software (S/W) code was developed as part of the radio science activities connected to the future ESA BepiColombo and ExoMars missions. After a short description of the algorithms used in the S/W code developed, the paper will reports the results of an intensive test campaign for the qualification of the S/W breadboard. The GPS-based delay estimations have been compared with the ESA microwave radiometer (MWR) measurements performed at the atmospheric remote sensing station of Cabauw, The Netherlands, of the KNMI (Dutch Meteorological Office) by ESA/ESTEC in the framework of the National Dutch CESAR project. The same GPS data has been processed by the KNMI data analysis centre and further comparisons have been undertaken with the UniBo GNSS S/W results.