It’s common to create temporary directories for tests, ideally a unique
directory per test to run them concurrently.
I’d like to propose adding `ExUnit.Callbacks.tmp_dir!/0` and this is how we
could use it:
defmodule MyTest do
use ExUnit.Case, async: true
test "my test" do
assert tmp_dir!() =~ "my test"
assert File.dir?(tmp_dir!())
end
end
The directory is lazily created on the first call, the second call to that
function within the same test simply returns the same path.
While the path must be unique per test, I believe it should also be predictable
to ease debugging, I picked: tmp/<module>/<test>.
To extract the module & test name, we have two options:
1. Define tmp_dir!/0 as a regular function and use stack trace
2. Define tmp_dir!/0 as a macro
Here’s a proof of concept for option 1:
- the code:
https://github.com/wojtekmach/elixir/commit/4c399540802a3cae583c086d865dc90d865df6c8
- example of usage in Elixir test suite:
https://github.com/wojtekmach/elixir/commit/01df2551582dd9acdaa2f6ff982d6767763070f1
The downside of using stack trace is it can easily get mangled, people
shouldn’t do this:
test "my test" do
tmp_dir!()
Task.async(fn ->
tmp_dir!()
end)
|> Task.await()
end
And instead do that:
test "my test" do
tmp_dir = tmp_dir!()
Task.async(fn ->
tmp_dir
end)
|> Task.await()
end
I believe documenting this might be enough.
This proposal is inspired by https://github.com/golang/go/issues/35998.
Any feedback appreciated!
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