Brake-by-wire is an innovative braking system that replaces the traditional hydraulic braking system with an electronic-hydraulic one. The brake-by-wire system is a safety-critical system that requires reliable and efficient communication between the electronic control units (ECUs) in the vehicle. Testing the communication network is critical to ensure the system's safety, reliability, and performance. Vector toolchain provides an efficient and reliable platform for testing the communication network of brake system ECUs. In this research, we present a testing methodology for ECUs in the Vector toolchain environment using Hardware-In-the-Loop (HIL) simulation. The proposed methodology includes the design of test scenarios, the implementation of the test cases, and the analysis of the test results. The results of the research show that the proposed methodology can effectively test the communication network of brake-by-wire ECUs in the Vector toolchain environment and provide insights into the network's performance and reliability.