To test Starfield, Bethesda gave the team a build that was "basically done" last year and said "this should be the game you're playing over the holiday"

gamesradar.com:

Bethesda boss Todd Howard says Starfield was "basically done" by holiday 2022, and to help test the mammoth RPG, virtually everyone on the development team got a build to play on their own Xbox consoles and PCs at home.

In a new Game Maker's Notebook interview with Insomniac Games CEO Ted Price, Howard discusses the final year of Starfield's development and the team-wide polish that came of it. Price asks how you test a massive RPG like Starfield, and Howard says "you take a long time and a lot of people."

"Our QA staff is awesome here, and the whole team tests," he continues. "One of our goals last holiday was – everybody went home for holiday break and the game was basically done. There were bugs, but here's a full game, you can play it – we flighted it on the retail Xbox. You can play it at home on your Xbox and your PC, and this should be the game you're playing over the holiday. The whole team, we tested the game really all year just playing it all the time, tweaking it, fixing I don't want to say how many bugs that our games create. We had a lot of QA help.

"It does help understanding what kind of bugs your game can create and then seeing patterns, using systems to go through the data. We do use some automated systems that run through every space in the game and then get a report. Here's where it was slow, here's where it crashed, here's where something else went wrong. We can focus more on the systemic gameplay. Here's 10 ways to break this quest. 

"We're really happy with where we landed on this release. Given the scale of the game, I think the team did an amazing job. It's not perfect by any means. There are things we're obviously fixing and are gonna continue to fix. But given the scale of it, where we ended up