run_test() and UVM_TESTNAME

Three are two ways to provide testcase name:

1. In top module, run_test(<testcase_name>)
2. Command line argument, UVM_TESTNAME=<testcase_name>

So here we're calling run_test inside top module. Now this run_test is implemented inside the uvm_globals.svh. This method is not defined in any class, this is a method defined in package.

Inside uvm_globals.svh :
--------------------------------------------------------------------------------
task run_test (string test_name="");
  uvm_root top;
  top = uvm_root::get();
  top.run_test(test_name);
endtask
--------------------------------------------------------------------------------
This run_test() is calling run_test of uvm_root and here name of testcase is getting stored inside "test_name" variable.

Implementation of command-line UVM_TESTNAME is also done inside run_test() of uvm_root.

Inside uvm_root file:

--------------------------------------------------------------------------------
task uvm_root::run_test(string test_name="");
...
  test_name_count = clp.get_arg_values("+UVM_TESTNAME=", test_names);

  // If at least one, use first in queue.
  if (test_name_count > 0) begin
    test_name = test_names[0];
    testname_plusarg = 1;
  end
...
endtask
--------------------------------------------------------------------------------

So whenever we pass UVM_TESTNAME it will be stored inside the "test_name" variable of uvm_root, which means if we have passed testcase name using run_test(), it will be overwritten by testcase name passed through UVM_TESTNAME.

Example:
--------------------------------------------------------------------------------
module top();
...
initial begin
run_test("my_test");
end
endmodule: top
--------------------------------------------------------------------------------

Testname passed through command line argument:

--------------------------------------------------------------------------------

./simv +UVM_TESTNAME=user_test

--------------------------------------------------------------------------------

If we have passed testcase name using both the above methods, user_test will be run as it is passed through command line argument.

PS:: Not only run_test() but global_stop_request(), set_global_timeout() [and many more] are also implemented inside uvm_globals.svh