State the Use parameters and parameter definition modules.

Parameters aren't preprocessor definitions and they have scope (for example parameters are associated with specific modules). Parameters  are hence more clean, and if you are in the habit of using a lot of defines; consider switching to parameters. As an instance, let's say we have a test (e.g. test12) that needs many parameters to have specific settings. In your code, you might have this sort of stuff:

module testbench_uart1 (....) 

parameter BAUDRATE = 9600;

...

if (BAUDRATE > 9600) begin

... E.g. use parameter in your code like you might any general variable

... BAUDRATE is completely local to this module and this instance. You might

... have the same parameters in 3 other UART instances and they'd all be different

... values...

Now,  your  test12  has  all  sorts of  settings  required  for  it.  Let's  define  a  special  module  known as testparams  that specifies  all  these  settings.  It  would itself  be  a  module  instantiated  under  testbench:

module testparams;

defparam testbench.cpu.uart1.BAUDRATE = 19200;

defparam testbench.cpu.uart2.BAUDRATE = 9600;

defparam testbench.cpu.uart3.BAUDRATE = 9600;

defparam testbench.clockrate CLOCKRATE = 200; // Period in ns.

... etc ...

endmodule

Above  module  always  has  same  module  name  though you  would  have  many  different filenames;  one  for  each  test.  So,  above  would  be  kept  in  test12_params.v.  Your  Makefile includes appropriate  params file given desired make target. (BTW: You may run across this sort of approach by ASIC vendors who might have a module containing parameters for a memory model or you might see this used to collect together a large number of system calls which turn off timing or warnings on particular troublesome nets, etc.)