atomkirk
Assert a list of patterns ignoring order
Do you think theres a way to write a function that matches a list of patterns with a list of values ignoring order? We use UXID and insert_all in our code a lot (which means all the inserted_at values are the same), which means theres not many options for guaranteeing sort order of results for doing assert […, …] = Repo.all(Model) which means tests are flakey. I just want to test “Records with these shapes were inserted into the db” and I don’t care about order.
@josevalim per https://twitter.com/josevalim/status/1493725996276760582
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josevalim
Here is a macro (with tests) that matches all elements in the collection matches exactly one pattern in the list:
defmodule ListAssertions do
defmacro assert_unordered(patterns, expression) when is_list(patterns) do
clauses =
patterns
|> Enum.with_index()
|> Enum.flat_map(fn {pattern, index} ->
quote do
unquote(pattern) -> unquote(index)
end
end)
clauses =
clauses ++
quote do
_ -> :not_found
end
quote do
ListAssertions.__assert_unordered__(
unquote(Macro.escape(patterns)),
unquote(expression),
fn x -> case x, do: unquote(clauses) end
)
end
end
def __assert_unordered__(patterns, enum, fun) do
result =
Enum.reduce(enum, %{}, fn item, acc ->
case fun.(item) do
:not_found ->
raise ArgumentError,
"#{inspect(item)} does not match any pattern: #{Macro.to_string(patterns)}"
index when is_map_key(acc, index) ->
raise ArgumentError,
"both #{inspect(item)} and #{inspect(acc[index])} match pattern: " <>
Macro.to_string(Enum.fetch!(patterns, index))
index when is_integer(index) ->
Map.put(acc, index, item)
end
end)
if map_size(result) == length(patterns) do
:ok
else
raise ArgumentError,
"expected enumerable to have #{length(patterns)} entries, got: #{map_size(result)}"
end
end
end
ExUnit.start()
defmodule ListAssertionsTest do
use ExUnit.Case, async: true
import ListAssertions
test "all match" do
assert_unordered([:foo, :bar, :baz], [:foo, :baz, :bar])
assert_unordered([{:ok, _}, {:error, _}], [{:error, :bad}, {:ok, :good}])
end
test "duplicates" do
assert_unordered([{:ok, _}, {:error, _}], [{:error, :bad}, {:ok, :good}, {:ok, :bad}])
end
test "too few" do
assert_unordered([{:ok, _}, {:error, _}], [{:error, :bad}])
end
test "unknown" do
assert_unordered([{:ok, _}, {:error, _}], [:what])
end
end
Better error messages that integrate nicely with ExUnit are left as an exercise to the reader. ![]()
LostKobrakai
It might sound dump, but if your data has no fixed order, then do not use assertions, which require order. Enum.find can do that for example. Testing for the length of lists can also make sure you‘re not missing records or have additional ones.
Sebb
You could find some inspiration here:
https://github.com/devonestes/assertions/blob/8b353fd941baee8b71181d4e8722c587a5aede87/lib/assertions.ex#L264
just make it take a list of maps to match agains your values.
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