Playing the devil's advocate - if one wants to be sure that os.Exit can't interfere with defers, what about something like:

func TestMain(m *testing.M) { os.Exit(testMain(m)) }

func testMain(m *testing.M) int {
     defer testhelper.Cleanup()
     return m.Run()
}

I understand that this is more verbose, but I'm wondering if that offsets adding extra code and documentation to the testing package. I would definitely agree with you if the testing package was designed from the ground up, however. Unless there is a specific reason for os.Exit that we are both missing.

@mvdan os.Exit is required to indicate tests success or failure iirc.

@OneOfOne what is your point? The integer that you can use in an os.Exit call is the same integer that @rogpeppe suggests to have as a return parameter. See my silly workaround above as an example.

TestMain is already a rare need. It doesn't make much sense to stack another one on top, especially when you can do what @mvdan suggests.