I think most HN users are not familiar with the pre-silicon verif environment, and so, don’t understand what a testbench is. I am fairly familiar with it, and I think I debugged testbench issues at some point, and I don’t really know what it is either.

But I’ll give it a shot, more informed users please correct me.

The testbench is a wrapper that turns command line options into binary file arrangements consumed by the simulator. For example, you could have a flag like -FORCE_ALL_CLOCKS_ON. The simulator software doesn’t think on this level, you actually need some piece of verilog, maybe compiled into some sort of patch, that makes some enable bits do nothing.

The testbench is a wrapper that determines if a test has passed or failed. There may be complex criteria to determine this, mostly by parsing logs, but it could hook in to the simulator in a more sophisticated way too.

The testbench is a wrapper that can fuse multiple simulators, so if your core is in FPGA but you have an Ethernet model in high level software (probably SystemVerilog?) you need a shim to get them talking.

The testbench is what you execute at the command line when you want to execute your tests.

The testbench is probably more than that. Or maybe less.