A Feedback Shift-Register, FSR, (400; 500; 900) comprising: a plurality of cells i, i ∈ {0,1,..., N - 1}, each cell i having an associated state variable x i ∈ {0,1} which represents a current value of the cell and an associated Boolean feedback function f i: {0,1) N → {0,1} of type f i x 0, x 1,..., x N − 1 = x i + 1 ⊕ g i x 0, x 1,..., x N − 1, which determines how the state variable is updated, the FSR being characterized in that: the plurality of cells comprises: one or more observable cells, each observable cell being associated with a non-trivial feedback function implemented by a combinational logic circuit, and one or more controllable cells, the associated state variable of each controllable cell belonging to a dependence set of exactly one of the non-trivial feedback functions, wherein each cell may be a controllable cell or an observable cell, but not both, and wherein each controllable cell i is provided with a multiplexer (403; 423) being arranged for selecting either a predecessor cell i + 1 or a test value as input, and each observable cell is arranged for making available its current value as test response, and the FSR is adapted to: acquire at least one test vector T m, each test vector comprising test values t n, n ∈ {0,1,..., K}, wherein K + 1 is a size of the largest dependence set of all non-trivial feedback functions, and for each test vector: load the test vector into the controllable cells, wherein, for each non-trivial feedback function f i: the value of t 0 is loaded into the cell i + 1, and for all n ∈ (1,..., K}, the value of t n is loaded into the controllable cell corresponding to the n-th variable in the dependence set of g i, and evaluate, for each observable cell, the test response of the associated combinational logic circuit for the loaded test values, the test responses being indicative of a fault in the FSR. a plurality of cells i, i ∈ {0,1,..., N - 1}, each cell i having an associated state variable x i ∈ {0,1} which represents a current value of the cell and an associated Boolean feedback function f i: {0,1) N → {0,1} of type f i x 0, x 1,..., x N − 1 = x i + 1 ⊕ g i x 0, x 1,..., x N − 1, which determines how the state variable is updated, the FSR being characterized in that: the plurality of cells comprises: one or more observable cells, each observable cell being associated with a non-trivial feedback function implemented by a combinational logic circuit, and one or more controllable cells, the associated state variable of each controllable cell belonging to a dependence set of exactly one of the non-trivial feedback functions, the plurality of cells comprises: one or more observable cells, each observable cell being associated with a non-trivial feedback function implemented by a combinational logic circuit, and one or more controllable cells, the associated state variable of each controllable cell belonging to a dependence set of exactly one of the non-trivial feedback functions, one or more observable cells, each observable cell being associated with a non-trivial feedback function implemented by a combinational logic circuit, and one or more controllable cells, the associated state variable of each controllable cell belonging to a dependence set of exactly one of the non-trivial feedback functions, acquire at least one test vector T m, each test vector comprising test values t n, n ∈ {0,1,..., K}, wherein K + 1 is a size of the largest dependence set of all non-trivial feedback functions, and for each test vector: load the test vector into the controllable cells, wherein, for each non-trivial feedback function f i: the value of t 0 is loaded into the cell i + 1, and for all n ∈ (1,..., K}, the value of t n is loaded into the controllable cell corresponding to the n-th variable in the dependence set of g i, and evaluate, for each observable cell, the test response of the associated combinational logic circuit for the loaded test values, the test responses being indicative of a fault in the FSR. load the test vector into the controllable cells, wherein, for each non-trivial feedback function f i: the value of t 0 is loaded into the cell i + 1, and for all n ∈ (1,..., K}, the value of t n is loaded into the controllable cell corresponding to the n-th variable in the dependence set of g i, and the value of t 0 is loaded into the cell i + 1, and for all n ∈ (1,..., K}, the value of t n is loaded into the controllable cell corresponding to the n-th variable in the dependence set of g i, and evaluate, for each observable cell, the test response of the associated combinational logic circuit for the loaded test values, the test responses being indicative of a fault in the FSR.