## 2 State of the Art  
Inspecting the condition of equipment such as rail traffic control devices that face specific requirements with regard to their operational safety and reliability is one of the most important tasks occurring at every life cycle stage. The functional fitness of RTC devices, wherein the devices fulfil their tasks, can be determined solely based on inspecting the behaviour of the equipment in the course of its operation or of conducted functional tests that give an image of the system's condition. Currently, functional tests are executed within the process of device operation and obtaining a 'permit to use' certificate, which has been thoroughly defined by Regulation [1], and to assess the conformity of structural subsystems with technical specifications for inter operability (TSI). Furthermore, the issue of testing is addressed in numerous documents by railway infrastructure administrators in the form of manuals regarding diagnostics, operation, commissioning, etc. Unfortunately, these manuals rather imprecisely define the functional state of RTC devices and generalize the scope of trials to be included in state assessment. Certification tests are aimed at obtaining a certificate of approval for use covering new equipment introduced into the Polish market, and they are conducted pursuant to Regulation [1]. The specified scope of required tests contains detailed requirements in terms of conducting functional tests under nominal conditions, under the impact of damage, and under environmental conditions consistent with the conditions of use. Required tests are mainly aimed at checking operational safety, and their results are verified by functional, reliability and safety tests usually conducted under actual operating conditions. Contemporary railway traffic control computer systems are usually designed as configurable, i.e., configured through application data. A system is recognized as configurable if the same computer equipment and its base software (which constitutes the hardware and software platform of the system) can be applied to construct functionally different systems and be deployed at various sites. The base (generic) product is used to construct RTC systems in different countries, so the safety of the base (generic) product has been checked, demonstrated and documented thoroughly. Introducing a base product onto the Polish market requires adopting it to domestic traffic management requirements, such as, among others, signalling principles (base application data), thus satisfying the functional requirements that devices of a specific class are faced with. In contrast, on-site (station, route) system installation requires applying specific data that takes into account the topology, traffic conditions and system environment. RTC systems have to meet the safety requirements of the highest SIL 4 level, which limits the possible interference with their structure. System complexity means that the basic test form is functional tests, which involve assessing the system response to actions generated by the operator and system environment, as well as random events of disturbance and damage nature. Therefore, the objective of these studies is to check all system functionalities in terms of conformity with the Polish railway network traffic management and signalling principles with regard to the base application [2]. In addition, the tests are conducted to check the conformity with safety principles set out in normative documentation [3; 4; 5]. A different group of tests are those executed as part of a specific application acceptance and commissioning process. Such tests cover newly installed and retrofitted devices and are undertaken as well after modernizing equipment at adjacent signal block posts (impact on functionality), and in the event of repairs or component replacement. Newly installed devices must be tested in terms of implementing all built-in functions within a given facility. This involves testing a specific application adapted solely to a specific traffic post.