use cider debugging inside a deftest

I'd like to debug my test when it is run by CIDER:

(let [test-system (atom (new-test-system))]
 (some-setup-code)
 (deftest my-test
   ;uses test-system in here)

As you see, my tests are wrapped in a let, which gets debugged as normal: I can hit c to move through the forms until it gets to the deftest, then the debugger quits, and my-test is highlighted in red, ready to be debugged when run.

When I run the test with , t t it doesn't debug, it passes as normal. I expected it to break and let me debug inside the test.

What am I doing wrong? I'm rather new to CIDER.