Devs MUST test
1) If you are aware of the costs yourself, you are much more likely to avoid mistakes in the first place.
2) If you write the test before you write the code, you are MUCH more likely to write proper code.
3) If you write the test before you write the code, you are MUCH less likely to write code with needless functionality (which will break needlessly and inopportunely.)
Sorry if you haven't learned these things yet, but untested == broken. Far more time is lost sending code back & forth than would be taken by having the devs do TDD.
The test team should be made up of senior devs whose minds are sufficiently warped to think about the nasty things that should not happen but do.