It's simply not possible to test that. This much is obvious if you've thought deeply about the nature of rocket testing.
You MUST fly to _really_ test.
Is there a good way that you're aware of to simulate the acceleration experienced by a rocket?
You're talking about a turbopump spinning at several tens of thousands of rpms, at very high temperature. Yes, a couple g's of lateral acceleration adds a bit too those stresses, but it's a fairly minor effect, I'm sure.
I think it's vastly more likely they're cracking from the rotation speed, temperature, and pressure.
I expect this is true, but I'd like to have a whole lot more information than the article contains. Specifically, under what conditions the cracks are observed.
The cracks were observed during ground testing, several years ago.