on_exit is guaranteed to run *after* the test process finishes. It is impossible to guarantee that something runs before it exits, due to links.
On Sat, Nov 12, 2022 at 23:55 Anthony Accomazzo <anth...@sequin.io> wrote: > Hey all, > > As I understand it, the `on_exit/2` callback is *not* guaranteed to > complete before a test process exits *if the test has a failure*. For > example, consider this flow: > > ``` > 1. Boot a process tree (Supervisor with child processes) > 2. Register an `on_exit/2` callback to stop the Supervisor > 3. Make an assertion -- the assertion fails > ``` > > Here, the assertion failure will crash the test process before `on_exit/2` > runs. > > Assuming I'm understanding this correctly, let me share a very common pain > point for our team. A test will fail, and we'll see an output like this: > > ``` > ** (Mox.UnexpectedCallError) no expectation defined for MyMock.some_func/0 > > 1) some failing test > match (=) failed > :ok = Module.some_operation() > ``` > > The issue is that we get error output *that was actually a result of the > test pid being torn down before the process tree*. So, it's a red herring. > There was *another* bug that caused the assertion to fail. In this case, > the Mox.UnexpectedCallError just happened because the test_pid went DOWN > while the process tree was still running, and they called a mock registered > to that test_pid and failed. > > However, in certain situations, it's super hard to know if the error > output is signal or noise. > > You can imagine that in the place of a Mox error, we have the same > situation with database connections, no_procs when we try to send signals > back to a dead test_pid, etc. > > We think it would be ideal to be able to register a callback that will > always run before a test_pid exits, regardless of if the test ran > successfully or not. > > What do you think? Or what other strategies might we employ? > > Thanks, > Anthony > > -- > You received this message because you are subscribed to the Google Groups > "elixir-lang-core" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to elixir-lang-core+unsubscr...@googlegroups.com. > To view this discussion on the web visit > https://groups.google.com/d/msgid/elixir-lang-core/52c85fb1-6a4e-4646-910f-aeb95ec90efdn%40googlegroups.com > <https://groups.google.com/d/msgid/elixir-lang-core/52c85fb1-6a4e-4646-910f-aeb95ec90efdn%40googlegroups.com?utm_medium=email&utm_source=footer> > . > -- You received this message because you are subscribed to the Google Groups "elixir-lang-core" group. To unsubscribe from this group and stop receiving emails from it, send an email to elixir-lang-core+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/elixir-lang-core/CAGnRm4KQe5iy2_vSviUNo5Eb3Kx1yQfti9EHwEYZLtgevyzsAw%40mail.gmail.com.
