It turns out that writing tests that contain subtests should probably be
limited to table-based tests and tests that share a common setup shared
between tests.

Writing tests with a subtest like this:

func TestSomething(t *testing.T) {
	t.Run("Subtest", func(t *testing.t) {})
}

Has the following disadvantages:

• It can lead to multiple tests failing with (unknown) status when
  only one of the subtests hang (never exit)
• In Go 1.20rc1, using t.Setenv is no longer allowed if the parent
  test is parallel

This is from Go 1.20rc1, trying to run the agent tests:

--- FAIL: TestAgent (0.00s)
    --- FAIL: TestAgent/Session_TTY_MOTD (0.00s)
panic: testing: t.Setenv called after t.Parallel; cannot set environment variables in parallel tests [recovered]
	panic: testing: t.Setenv called after t.Parallel; cannot set environment variables in parallel tests

It's unclear if the above is a Go bug or not, but I've (and maybe others) have observed in the past that t.Setenv isn't always behaving as expected. This could potentially be the source of that confusing behavior.