Method for applying a patch to a virtualized network function (VNF A) in order to test the updating of said virtualized network function that is included in a first virtual network (VN A), a network hypervisor being interfaced between the first virtual network and a set of at least one hardware resource capable of supplying necessary resources to said first virtual network, said method, implemented by the network hypervisor, comprising: - identifying a set of dependent virtualized network functions included in the first virtual network, said set comprising at least the virtualized network function to be updated and at least one network function functionally dependent on said network function to be updated, - creating a second virtual network (VN B) called a "virtual test network", said virtual test network comprising clones of virtual machines implementing the dependent virtualized network functions of the set, said cloned virtual machines forming clones of the dependent virtualized network functions of the set, the cloned virtual machines having a system state identical to that of the virtual machines implementing the dependent virtualized network functions of the set in the first network, - interconnecting, in the virtual test network, clones of the dependent virtualized network functions of the set, said interconnection being identical to an interconnection in the first network of the dependent virtualized network functions of the set, - identifying at least one input data packet of a virtualized network function of the set of dependent virtualized network functions, duplicating said identified packet and routing said duplicated packet to the virtual test network, - applying the patch to the clone of the virtualized network function to be updated in the test network, - collecting and comparing (E6, E7) values of at least a first and a second performance indicator, a first indicator measuring a performance value on a virtualized network function of the set during the routing of input packets of said virtualized network function in the first virtual network and a second indicator measuring the performance value on the clone of the corresponding virtualized network function during the routing of duplicated input packets of the corresponding virtualized network function in the virtual test network, an alert being triggered when the values of the first and second indicators differ. - identifying a set of dependent virtualized network functions included in the first virtual network, said set comprising at least the virtualized network function to be updated and at least one network function functionally dependent on said network function to be updated, - creating a second virtual network (VN B) called a "virtual test network", said virtual test network comprising clones of virtual machines implementing the dependent virtualized network functions of the set, said cloned virtual machines forming clones of the dependent virtualized network functions of the set, the cloned virtual machines having a system state identical to that of the virtual machines implementing the dependent virtualized network functions of the set in the first network, - interconnecting, in the virtual test network, clones of the dependent virtualized network functions of the set, said interconnection being identical to an interconnection in the first network of the dependent virtualized network functions of the set, - identifying at least one input data packet of a virtualized network function of the set of dependent virtualized network functions, duplicating said identified packet and routing said duplicated packet to the virtual test network, - applying the patch to the clone of the virtualized network function to be updated in the test network, - collecting and comparing (E6, E7) values of at least a first and a second performance indicator, a first indicator measuring a performance value on a virtualized network function of the set during the routing of input packets of said virtualized network function in the first virtual network and a second indicator measuring the performance value on the clone of the corresponding virtualized network function during the routing of duplicated input packets of the corresponding virtualized network function in the virtual test network, an alert being triggered when the values of the first and second indicators differ.