flat_errors_on/3: ensure field exists

CHANGELOG.md

@@ -1,5 +1,11 @@
 <!-- SPDX-License-Identifier: Apache-2.0 -->
 
+## Unreleased
+
+### Added
+
+* Ensure field/assoc/embed exists when listing errors in `flat_errors_on/3`. This prevents accidental test passes on typos in assertions like `refute_errors_on(cs, :sommtypo)`.
+
 ## [1.0.0] - 2023-12-21
 
 No changes from v0.17.0.

lib/bitcrowd_ecto/assertions.ex

@@ -43,7 +43,9 @@ defmodule BitcrowdEcto.Assertions do
   @doc since: "0.1.0"
   @spec flat_errors_on(Changeset.t(), atom) :: [String.t() | atom]
   @spec flat_errors_on(Changeset.t(), atom, [{:metadata, atom}]) :: [String.t() | atom]
-  def flat_errors_on(changeset, field, opts \\ []) do
+  def flat_errors_on(%Changeset{} = changeset, field, opts \\ []) when is_atom(field) do
+    assert_field_or_assoc_or_embed(changeset, field)
+
     metadata =
       opts
       |> Keyword.get(:metadata, [:constraint, :validation])
@@ -66,6 +68,23 @@ defmodule BitcrowdEcto.Assertions do
     end)
   end
 
+  defp assert_field_or_assoc_or_embed(%Changeset{} = changeset, field) when is_atom(field) do
+    assert_field_or_assoc_or_embed(changeset.data, field)
+  end
+
+  defp assert_field_or_assoc_or_embed(%{__struct__: schema}, field) when is_atom(field) do
+    fields_and_assocs_and_embeds =
+      List.flatten([
+        schema.__schema__(:fields),
+        schema.__schema__(:associations),
+        schema.__schema__(:embeds)
+      ])
+
+    assert field in fields_and_assocs_and_embeds,
+      message:
+        "Trying to access #{inspect(field)} on #{inspect(schema)}, but it is not a field, association, or embed."
+  end
+
   @doc """
   Asserts that a changeset contains a given error on a given field.
 

test/bitcrowd_ecto/assertions_test.exs

@@ -30,6 +30,12 @@ defmodule BitcrowdEcto.AssertionsTest do
       assert :bar in flat_errors_on(cs, :some_string, metadata: :foo)
       assert :bar in flat_errors_on(cs, :some_string, metadata: [:foo])
     end
+
+    test "fails when trying to list errors for a field/assoc/embed that does not exist" do
+      assert_raise ExUnit.AssertionError, ~r/not a field/, fn ->
+        assert flat_errors_on(changeset(), :doesnotexist)
+      end
+    end
   end
 
   describe "assert_error_on/4" do