Factory Overrides in Tests: Explicit, Local, Reviewable

Override intent and scope

Use factory overrides to switch behavior without rewriting env code, but keep overrides localized and discoverable .

[TEST][UVM] override scope ladder

global (discouraged for scenario tests)
  set_type_override_by_type

instance (preferred)
  set_inst_override_by_type("env.agt*.drv")

late dynamic override
  avoid unless debugging special-case behavior

virtual function void apply_factory_overrides();
  my_driver::type_id::set_inst_override(
    debug_driver::get_type(),
    "uvm_test_top.env.agt_tx.drv"
  );
endfunction

function void build_phase(uvm_phase phase);
  super.build_phase(phase);
  apply_factory_overrides();
endfunction

Key takeaways

• Instance overrides preserve scenario isolation.

• Apply overrides before component creation in build_phase.

• Log active overrides every test run.

Common pitfalls

• Silent global overrides leaking into unrelated tests.

• Applying overrides after env creation.

• No audit trail linking override to scenario intent.

Override hygiene and diagnostics

Treat factory behavior as part of test API; failures are often override-scope mistakes.

Override report snippet

function void report_overrides();
  uvm_factory f = uvm_factory::get();
  f.print(1);
endfunction

[TEST] override sanity checklist

- expected class replaced?
- expected instance path matched?
- one scenario, one override purpose?
- regression seed reproduces replacement?

Conflict management

• Avoid setting same instance override in multiple helper methods.

• Keep override definitions near scenario configuration.

• Use dedicated debug tests for broad experimental overrides.

[UVM][TEST] conflict pattern

base_test applies override A
child_test applies override B on same target
result:
  last-writer wins, intent becomes unclear

fix:
  centralize in apply_factory_overrides() with explicit ordering

Common pitfalls

• Interleaving override setup with randomization side effects.

• Relying on class-name strings instead of type-safe handles.

• No CI guard to detect accidental global override additions.