atomkirk

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

Most Liked

josevalim

josevalim

Creator of Elixir

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. :slight_smile:

23
Post #7
LostKobrakai

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

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.

Last Post!

josevalim

josevalim

Creator of Elixir

At the moment I don’t think it is ExUnit.Assertions material but I will keep an eye open for more use cases!

Where Next?

Popular in Questions Top

joaquinalcerro
Hi there, I am working with Ecto-Postgresql and I need to call all of the records from a specific table but the table has 40,000 records...
New
hariharasudhan94
lets say i have a sample like a = 20; b = 10; if (a &gt; b) do {:ok, "a"} end if (a &lt; b) do {:ok, b} end if (a == b) do {:ok, "equa...
New
jononomo
For some reason my phoenix channels are working for me in my local dev environment, but as soon as I deploy via Docker, I get a 403 error...
New
lastday4you
I wanted to check elixir version in phoenix because i found that my elixir is 1.5 but when i use Enum.chunk_by it said the function is un...
New
dblack
I’ve got an issue with an app and I’ve no idea of how to troubleshoot it. I’m hoping someone here might have seen something similar. I p...
New
senggen
Erlang/OTP 25 [erts-13.2.2] [source] [64-bit] [smp:8:8] [ds:8:8:10] [async-threads:1] 15:22:35.803 [error] gen_event {lager_file_backend...
New
jason.o
In the code below, if the create action is not set to accept “extra_key” as an input, it errors out with a message shown above. Is there ...
New

Other popular topics Top

nobody
Hi! In PHP: $_SERVER[‘SERVER_ADDR’] - in Elixir? Searched the docs for ip address and the web, no good results. Thanks!
New
lanycrost
Hi everyone! I need implement if…else if…else condition from my elixir code, and anymore of this control flow structures not work proper...
New
stefanchrobot
What’s the safe way to decode a JSON string into a struct? I want to avoid calling String.to_atom. Jason.decode can give me a map with st...
New
gshaw
What is the idiomatic way of matching for not nil in Elixir? E.g., First way: defp halt_if_not_signed_in(conn, signed_in_account) when...
New
msaraiva
Surface is an experimental library built on top of Phoenix LiveView and its new LiveComponent API that aims to provide a more declarative...
564 44265 214
New
dblack
I’ve got an issue with an app and I’ve no idea of how to troubleshoot it. I’m hoping someone here might have seen something similar. I p...
New

We're in Beta

About us Mission Statement