Scenario Inheritance: Specialize Intent, Not Infrastructure

Inheritance model

Use inheritance to express what changes per scenario , while inherited behavior preserves infra consistency.

[TEST][UVM][ENV] inheritance stack

base_test
  ├─ smoke_test
  ├─ error_injection_test
  ├─ burst_traffic_test
  └─ low_power_resume_test

all derived tests share:
  env build policy
  timeout policy
  report formatting

class burst_traffic_test extends base_test;
  `uvm_component_utils(burst_traffic_test)

  virtual function void configure_scenario();
    super.configure_scenario();
    cfg.txn_count = 2000;
    cfg.enable_backpressure = 1;
  endfunction

  virtual task run_main_sequence();
    burst_vseq seq = burst_vseq::type_id::create("seq");
    seq.start(env.v_sqr);
  endtask
endclass

Key takeaways

• Derived tests should read like scenario docs.

• Call super methods unless intentionally replacing behavior.

• Prefer cfg knobs over direct env internals in child tests.

Common pitfalls

• Overriding build_phase in child tests without strong reason.

• Duplicating run_phase in every child test.

• Changing infrastructure defaults in scenario classes.

Scenario taxonomy patterns

Define scenario families so coverage planning and regression slicing are predictable.

Family matrix

[TEST] scenario family map

smoke/*        -> short sanity tests (<1 min)
protocol/*     -> legal/illegal protocol behaviors
stress/*       -> long random and throughput scenarios
power/*        -> reset/clock/power transition coverage
debug/*        -> high-verbosity issue repro tests

• Use naming convention to derive testlist filters.

• Keep one owner per family for review accountability.

• Limit inheritance depth to two levels in most projects.

Extension-point policy

virtual function void set_scenario_id(string id);
  scenario_id = id;
endfunction

virtual function void configure_sequences();
  // choose sequence classes and base constraints
endfunction

[TEST][ENV] policy

allowed child overrides:
  configure_scenario
  configure_sequences
  optional run_main_sequence

discouraged child overrides:
  build_phase
  connect_phase
  objection management

Common pitfalls

• Deep class trees that obscure active behavior.

• Scenario IDs embedded only in class names, not logs.

• No documented override policy for new contributors.