In real-time control of electric grids using multiple software agents, the control performance depends on (1) the proper functioning of the software agents, i.e., absence of software faults, and (2) the behavior of software agents in the presence of non-ideal communication networks such as message losses and delays. To evaluate the control performance of such systems, we propose T-RECS, a virtual commissioning tool. T-RECS enables testing the performance of software-based control in-silico (before the actual deployment of software agents in the grid), saving both time and money. Developers can run the binaries of their software agents in T-RECS where these binaries exchange real messages by using an emulated network and simulated models of the electric grid and resources. Consequently, the control of an entire microgrid can be tested on a standard computer. In this paper, we first describe the design and the open-source implementation of T-RECS. Second, we measure its CPU and memory usage and show that our implementation can accommodate eight software agents on a standard laptop computer. Third, we validate the simulated grid used in T-RECS by replaying data collected from experiments performed in a real low-voltage microgrid. We find that the average error is 0.037% and the 99th percentile of the error is less than 0.1%. Finally, we present some typical use-cases of T-RECS such as performance evaluation (1) under extreme grid conditions and (2) with non-ideal communication networks. The former, i.e., performance evaluation under extreme grid conditions, is difficult to test in the field due to safety concerns.