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diff --git a/test/support/data_case.ex b/test/support/data_case.ex
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+++ b/test/support/data_case.ex
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+defmodule MatrixAppService.DataCase do
+  @moduledoc """
+  This module defines the setup for tests requiring
+  access to the application's data layer.
+  You may define functions here to be used as helpers in
+  your tests.
+  Finally, if the test case interacts with the database,
+  it cannot be async. For this reason, every test runs
+  inside a transaction which is reset at the beginning
+  of the test unless the test case is marked as async.
+  """
+
+  use ExUnit.CaseTemplate
+
+  alias Ecto.Adapters.SQL.Sandbox
+  alias Ecto.Changeset
+  alias MatrixAppService.Repo
+
+  using do
+    quote do
+      alias MatrixAppService.Repo
+
+      import Ecto
+      import Ecto.Changeset
+      import Ecto.Query
+      import MatrixAppService.DataCase
+    end
+  end
+
+  setup tags do
+    :ok = Sandbox.checkout(Repo)
+
+    unless tags[:async] do
+      Sandbox.mode(Repo, {:shared, self()})
+    end
+
+    :ok
+  end
+
+  @doc """
+  A helper that transform changeset errors to a map of messages.
+      assert {:error, changeset} = Accounts.create_user(%{password: "short"})
+      assert "password is too short" in errors_on(changeset).password
+      assert %{password: ["password is too short"]} = errors_on(changeset)
+  """
+  def errors_on(changeset) do
+    Changeset.traverse_errors(changeset, fn {message, opts} ->
+      Enum.reduce(opts, message, fn {key, value}, acc ->
+        String.replace(acc, "%{#{key}}", to_string(value))
+      end)
+    end)
+  end
+end