Note that Go 1.10 has updated wording here:

current: https://golang.org/pkg/testing/#T.Run
go1.10: https://tip.golang.org/pkg/testing/#T.Run

go1.10 says:

Run runs f as a subtest of t called name. It runs f in a separate goroutine and blocks until f returns or calls t.Parallel to become a parallel test. Run reports whether f succeeded (or at least did not fail before calling t.Parallel).

Run may be called simultaneously from multiple goroutines, but all such calls must return before the outer test function for t returns.

That was added in d452986 for #22993.

Is that sufficient?

#22993 also bit me, and led to the code in this example that deadlocks.

I don't think the doc update is sufficient. There is still a critical bit of information missing:

its execution is suspended until its calling test function, that of the parent test, has returned.

Also hit this. There is definitely a lot more detail necessary in the doc for Parallel(). The fact that the test does not proceed until the parent finishes is very important and not at all obvious.

Also, what may not be obvious on first look:

func TestMain(t *testing.T) {
    setup()
    defer teardown()
    for name, tt := range testCases {
        t.Run(name, func(t *testing.T) {
            t.Parallel()
            doStuff()
        })
    }
}

doStuff() will NEVER be executed before the defer teardown() kicks in.
Using sync.waitGroup doesn't help with this either, because the subtests only run once the parent has finished.

Is there any possibility to make this "work as expected"?

@tommyknows That is best discussed in a forum, not on this issue. Let's not clutter up the issue. Thanks. https://golang.org/wiki/Questions.

@tommyknows put them in a group

func TestMain(t *testing.T) {
    setup()
    defer teardown()
    t.Run("group", func(t *testing.T) {
             for name, tt := range testCases {
                   t.Run(name, func(t *testing.T) {
                       t.Parallel()
                       doStuff()
                   })
           }
    })
}

https://go.dev/play/p/SlW20M84N_g