NOVELTY - System setup, comprises: (a) at least one digester with good agitation; (b) optionally at least one measuring device or sensor for measuring gas composition on-line or spot check in regular basis; (c) at least one container for chemical fixation of other gases than biomethane gas, where the other gas is at least carbon dioxide, and the chemical fixation is based on irreversible reaction; and (d) at least one gas flow measuring device. The digester is connected to container, which is in turn connected to gas flow measuring device, where (b) may be provided after digester and/or after container.    USE - The system setup is useful: for carrying out a biological methane potential test on a biosample; and for measuring biomethane gas in a biogas flow (all claimed); to build flow cell array (multi-flow cell arrangement); and as a standalone device to provide on-line, real-time monitoring of biogas production from small-scale biogas digesters.    ADVANTAGE - The system setup: has simple construction and modularized instrument design for all instrument components; does not require expensive techniques and instruments (gas chromatography and optical measurement); has flexible design; enables direct and continuous measurement of formed methane; does not need any membrane technology; can measure multi-channels of ultra low flow of methane gas simultaneously with high precision and very low cost; operates based on leverage effect which ensures high gas measuring accuracy; utilizes slow rotating agitator which minimizes analysis disturbance due to uneven release of biogas or poor mass transfer; and insures not only much more frequent data acquisition, but also high data quality to meet the demand for studying the dynamic information of degradation process.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for:    (1) system setup for measuring biomethane gas in a biogas flow, comprising: (c) and (d) as above per se, where the container is connected to the gas flow measuring device; and    (2) measuring the biological methane potential of a biosample, comprising: loading a feedstock to the digester with continuous good agitation; fermenting anaerobically in the digester; flowing the produced biogas to the container for chemical irreversible fixation, where the other gases than biomethane gas are fixated; and flowing the biomethane gas to the gas flow measuring device for measurement of the biomethane gas flow.    DESCRIPTION OF DRAWING(S) - The figure shows schematic representation of a process for an automated methane potential test using system setup.