Explain about run_test() in UVM

Execute all component’s all registered phases.

If the optional test_name argument is provided, or if a command-line plusarg, +UVM_TESTNAME=TEST_NAME, is found, then the specified component is created just prior to phasing.

The test may contain new verification components or the entire test-bench, in which case the test and test-bench can be chosen from the command line without forcing recompilation.

If the global (package) variable, finish_on_completion, is set, then run_test will call $finish after all phases are executed.

1. Take string name from plusarg (+UVM_TESTNAME ) or its own argument ,
1. if ($value$plusargs("UVM_TESTNAME=%s", test_name)) begin
2. Create uvm_test_top using below command
1. $cast(uvm_test_top, factory.create_component_by_name(test_name, "", "uvm_test_top", null));
3. Call m_run_phases of uvm_phase class,
1. Which execute all registered phases of all componenets in pre-defined order.
4. Wait for all phases to be completed,
5. If the global (package) variable, finish_on_completion, is set, then run_test will call $finish after all phases are executed.
1. By-default finish_on_completion bit is set to 1 only

Reference:

1) uvm_root.svh file from uvm source code