And to ensure it would not buckle, per the article.

Implying they were not sure it would not buckle, until they drove the trucks on.

Well, that's how it was reported, but not necessarily accurate.

They probably wanted to quantify how much the bridge moved in various ways. There were likely many "it probably won't move more than acceptable in this way, but if it does we've made it easy to add a change here to fix that" facets of the design. All large complex structures undergo testing like this, sea trials for ships being the quintessential example.

That's like saying unit testing implies there are bugs in the code.

If I was sure my code had no bugs, I would not need unit testing.

That's dubious. Unit tests make future development easier.

I'll trust the truck-test far more than any simulation.