The need to reduce vehicle emissions imposed by governments has led manufacturers to focus on the development of battery electric vehicles. Although this is a promising solution for improving air quality and reducing CO2 emissions, some limitations still hinder the widespread adoption of electric vehicles. The primary obstacle is the limited driving range compared to traditional internal combustion engine vehicles. This is due to the significant difference in energy density between the two technologies' energy storage systems and the longer charging time required for batteries compared to refuelling a tank of fuel. To address the limited driving range without increasing battery size (which would raise vehicle cost and weight), enhancing the energy efficiency of auxiliary systems, particularly the thermal management system, becomes crucial. Installing heat pumps and integrating them into a system that manages the thermal needs of the cabin, battery, power electronics and electric motor (PEEM) in a single unit can be an effective option for improving vehicle energy efficiency. The solution explored in this study is referred to as a single-liquid coolant loop. It consists of a primary refrigerant loop (a heat pump) that exchanges heat with a secondary liquid coolant loop. Through an intelligent valve system, the secondary loop delivers cold or hot coolant to various vehicle subsystems that require thermal management and allows for the recovery of the waste heat from the electronic components. Implementing control logic and defining the system's working modes necessitate simulating it using a mathematical model due to the high cost of conducting experimental tests on a real vehicle. To overcome the computational time required for simulating a model with a high level of accuracy, particularly regarding the refrigerant circuit, this paper presents the design of a hardware-in-the-loop (HIL) simulation. The HIL simulation allows testing the various functionalities of a vehicle-integrated thermal management system in real-time. The simulation focuses on the coolant loop and the models of cabin, battery, and PEEM, while a dedicated test bench replicates the thermal loads calculated in the simulation to evaluate the performance of the heat pump. The thermal loads are replicated by incorporating an electric heater into a coolant circuit connected to the evaporator and a radiator into a separate coolant circuit connected to the condenser. An important advantage of this HIL simulation is that we can verify the performance of the compressor's and electronic expansion valve's control systems on the real heat pump without assembling the entire vehicle thermal management system in the testing area. The results demonstrate the HIL system's ability to synchronize the test bench with the mathematical model by showcasing a battery electric bus driving in summer conditions. This HIL system demonstrates effective testing for the thermal management system of battery electric vehicles. However, certain limitations arise from the electric heater and radiator installed on the test bench. To accurately reproduce scenarios with the maximum thermal load on the evaporator, a more powerful electric heater is required. Similarly, for scenarios with the minimum thermal load on the condenser, without coolant temperature oscillations, a radiator with a smaller heat transfer area is needed. Addressing these hardware limitations would enhance the overall performance and accuracy of the HIL system for testing thermal management in electric vehicles.