test: add tests corresponding to #561

unable to reproduce

Author: zachdaniel

test/atomics_test.exs

@@ -40,6 +40,27 @@ defmodule AshPostgres.AtomicsTest do
              |> Ash.update!()
   end
 
+  test "an atomic update on decimals works" do
+    post =
+      Post
+      |> Ash.Changeset.for_create(:create, %{title: "foo", decimal: Decimal.new("1")})
+      |> Ash.create!()
+
+    assert %{decimal: result} =
+             post
+             |> Ash.Changeset.for_update(:subtract_integer_from_decimal, %{amount: 2})
+             |> Ash.update!()
+
+    assert Decimal.eq?(result, Decimal.new("-1"))
+
+    assert %{decimal: result} =
+             post
+             |> Ash.Changeset.for_update(:subtract_from_decimal, %{amount: Decimal.new("2")})
+             |> Ash.update!()
+
+    assert Decimal.eq?(result, Decimal.new("-3"))
+  end
+
   test "an atomic works on a constrained integer" do
     post =
       Post

test/support/resources/post.ex

@@ -184,6 +184,16 @@ defmodule AshPostgres.Test.Post do
       end)
     end
 
+    update :subtract_integer_from_decimal do
+      argument(:amount, :integer, allow_nil?: false)
+      change(atomic_update(:decimal, expr(decimal + -(^arg(:amount)))))
+    end
+
+    update :subtract_from_decimal do
+      argument(:amount, :decimal, allow_nil?: false)
+      change(atomic_update(:decimal, expr(decimal + -(^arg(:amount)))))
+    end
+
     update :add_to_limited_score do
       argument(:amount, :integer, allow_nil?: false)
       change(atomic_update(:limited_score, expr((limited_score || 0) + ^arg(:amount))))