add test for req (header) config

test/car_req_test.exs

@@ -848,7 +848,28 @@ defmodule CarReqTest do
       secret = "Token Shh, it's a secret"
       not_auth_header = [{"NOTauthorization", secret}]
       client = TestClientDupeHeaderImpl.client(headers: not_auth_header, auth: secret)
-      assert client.headers == not_auth_header
+      # header is downcased and converted to a map
+      assert client.headers == %{"notauthorization" => ["Token Shh, it's a secret"]}
+    end
+  end
+
+  describe "config" do
+    setup do
+      Application.put_env(:req, :legacy_headers_as_lists, true)
+    end
+
+    test "supports headers config option" do
+      Application.get_env(:req, :legacy_headers_as_lists) |> IO.inspect(label: "legacy_headers_as_lists")
+
+      defmodule TestClientLegacyHeaderImpl do
+        use CarReq
+      end
+
+      secret = "Token Shh, it's a secret"
+      not_mangled_auth_header = [{"NOTauthorization", secret}]
+      client = TestClientLegacyHeaderImpl.client(headers: not_mangled_auth_header, auth: secret)
+      # header is not mangled
+      assert client.headers == not_mangled_auth_header
     end
   end