# A Survey of Vehicle to Everything (V2X) Testing
## 5 V2X Testing Methods
### Conformance Testing  
Protocol conformance is the basis of V2X communication. Only by meeting the protocol conformance can we ensure the interoperability between vehicles, pedestrians, RSU, cloud platform, and other participants, which is the basis for developing various types of V2X applications. The protocols can be divided into two major categories. One is the communication protocol, which stipulates the data format and interaction flow of the communication processes in a V2X network, and the other is the security protocol, which stipulates the security processes such as certificates and authentication. Communication protocol conformance testing can ensure the interconnection and interoperability of devices [53], and security protocol conformance testing ensures security. Therefore, protocol conformance testing is a must-have requirement for all telematics devices. ETSI stipulates an abstract test system for V2X conformance testing [54]. There are many ways to implement this abstract test system. ETSI recommends using TTCN-3 [55] to implement the abstract test system, as shown in Figure 3. This implementation conforms to ISO 9646 [56]. 3 GPP provides a TTCN-3 based test system architecture [57], as shown in Figure 4, which is similar to the ETSI abstract test system. The difference is that the TTCN-3 test system (Host-PC in Figure 4) communicates with the device under test (UE in Figure 4) through the System Simulator hardware (HW). The test system is combined with the System Simulator HW, which is equivalent to a complete and controllable communication device that can fully test a device under test according to test cases by automatically or manually simulating communication processes. Figure 3: Abstract Test System [54]. In addition, ISO TS 20026 [58] also describes several similar ITS test architectures, which are generally indistinguishable from the above test architecture. In order to support the conformance testing and enhance the completeness, test specifications have been proposed. For example, the Certification Operating Council (COC) under the U.S. Department of Transportation has established a series of specifications for conformance testing. In China, the C-V2X WG under IMT-2020(5G) promotion group also have established specifications for conformance testing, function testing and etc. [PERSON] [59; 60] designed a set of tools that could be used in order to check the conformance of a Cooperative-Intelligent Transport System (C-ITS). But there are still many challenges during the process of conformance testing. Firstly, due to the complexity of the standards, conformance testing needs to test every field in that standards which mean we need to design a large number of test cases. If a tester manually does a test, a lot of time will be wasted and there may be many mistakes during the testing process. So, the automated testing system has been developed. Its advantages are saving time and decreasing mistakes. But additional development needs to be done by the equipment developer because the automated testing system need control the device under test through a test control interface (TCI). The more complicated the test process is, the more additional development may be. So how to push the manufacturers to do the automated testing is a big question. Secondly, how many test cases are sufficient is another question. Test cases in conformance testing not only need to cover all the fields of the standards, but also need to test the understanding of the specific fields. For example, the representation and unit of longitude and latitude maybe differ. These confusions are mostly caused by the vague description in the standards and the conformance testing is a nice feedback to these standards. Finally, the above implements for conformance testing are all black-box, and they lack information or knowledge of system under test (SUT) [61]. Therefore we can't confirm whether a device under test transmits data by its protocol stacks.