Limits of Hand-Rolled Testbenches
Three real problems surfaced across this topic, each one hit directly rather than described abstractly. This page takes stock of exactly those three, and points at the specific, already-shipped page on this site that solves each one properly.
No override mechanism
Configuration and Reuse's component-swap dilemma had no comfortable answer: either edit environment's shared constructor for every new driver variant, or break the encapsulation environment was built around. Neither scales — a testbench with a dozen test-specific component variants either has a constructor riddled with if/else branches for every one of them, or has given up on the environment owning its own construction at all.
The UVM Factory is the direct fix: type_id::create() in place of new(), plus set_type_override()/set_inst_override(), lets a test redirect any create() call anywhere in the tree to a different class — without editing environment's source at all, and without needing to construct anything outside the environment first. Both of Option A and Option B's specific costs disappear at once, because the override happens at the one call site that already exists, not by threading a pre-built object in or hardcoding a branch.
No scoped configuration
The Virtual Interface Bridge threaded vif through a constructor argument by hand; Configuration and Reuse's tb_config class was the alternative — global, static, with every component seeing the identical value and no way to scope one instance differently from another.
Resource DB & Config DB solves both problems in one mechanism: uvm_config_db::set()/get() propagates configuration down an arbitrarily deep tree with no constructor threading, and it's genuinely scoped — a wildcard path can target "every component," or one exact instance, or anything in between. Neither the constructor-threading approach nor the global-static approach this topic used can do that middle ground at all.
No phase discipline
The Test's #100 before $finish was a flat guess at how long the driver/monitor/scoreboard needed to finish draining — right by luck at one transaction count, silently wrong (too short, truncating real checks, or wastefully long) the moment that count changes.
Phases & Objections's objection mechanism — raise_objection() before stimulus starts, drop_objection() only once it's genuinely finished — replaces the guess with an actual, correct signal: the phase stays open for exactly as long as real work is happening, and ends the instant it isn't, regardless of transaction count.
The pattern across all three
Every fix above is a specific, named answer to a specific, named problem this topic's own code ran into — not an abstract "UVM is more powerful" claim. That's the whole point of building this topic by hand before reading any of those pages: each one now lands as "the thing that fixes the exact wall I just hit," which is a different, more durable kind of understanding than reading about a factory or a config database cold.
What's next
Every piece this topic set out to build now exists on its own page. The last page assembles all of it — transaction, generator, driver, monitor, reference model, scoreboard, assertion checker, environment, and test — into one complete testbench, shown together the way it'd actually be designed.