A filter cassette and a method for allowing a leak to be detected are disclosed, in which the filter cassette comprises a main body defining a first chamber. The main body includes an inlet and an outlet, a filter separating the first chamber into first and second sub-chambers, the inlet being in fluid communication with the first sub-chamber and the second sub-chamber being in fluid communication with the outlet. The main body also includes a second chamber is defined by the main body and the filter, wherein in absence of a leak the second chamber is substantially not in fluid communication with the first chamber. The main body further includes a port in fluid communication with the second chamber, whereby measuring a fluid characteristic in the second chamber by means of the port allows a detection of a leak, i.e. an external leak or a bypass leakage.