sodapopcan
Perhaps oddly, this is the first time I’ve hit this situation in Elixir: I would like to test that a function has only been called once. My use-case is that I’m writing a wrapper around Ecto’s preload and I want to test that when given a list of structs, the implementation looks something like this:
def my_wrapper(structs, preloads) do
MyApp.Repo.preload(structs, preloads)
end
and not this:
def my_wrapper(structs, preloads) do
for struct <- struct do
MyApp.Repo.preload(struct, preloads)
end
end
My only idea so far is to create a mock for MyApp.Repo.preload (which is generally considered a no-no) and have it update a count stored in a gen_server every time it’s called. This is certainly a solution, but does anyone have any better ideas? I have looked at the tests for preload itself and did not come away with anything (although perhaps I didn’t look hard enough?)
Asking here before I resort to asking the robots.
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jhogberg
trace — OTP 29.0.2 (kernel 11.0.2) ought to do it, just trace it from your test case and make sure you get exactly one message saying it’s been called.
jstimps
Hi, I do this exactly in one of my projects with the trace module! The approach has been a huge help across multiple refactors, to keep performance solid. I love it so much that I wrote a blog post about it.
Asd
Its can be done in a very ergonomic way with Repatch
First, initialize Repatch in
test/test_helper.exsSecond, in test do something like
sodapopcan
I had a very “duh me” moment last night as I was falling asleep when I realized I asked this question while following along in in almost real time with this thread which mentions Repatch for spying.
That’s a great write-up @jstimps, thanks! I really need to start dipping into Erlang libs as these are things I’m aware of but never think to use.
I’m giving @Asd the check as even though it means adding a dependency, I’ve been meaning to give Repatch a try since it was announced and that API is so nice.
Thanks for the answers, all!