diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 8b0381d11..e35b4d29a 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -85,7 +85,7 @@ unit-testing:
   script:
     - mix ecto.create
     - mix ecto.migrate
-    - mix test --cover --preload-modules
+    - mix test --cover --preload-modules --warnings-as-errors
   coverage: '/^Line total: ([^ ]*%)$/'
   artifacts:
     reports:
diff --git a/test/pleroma/user/import_test.exs b/test/pleroma/user/import_test.exs
index b4efd4bb0..f75305e0e 100644
--- a/test/pleroma/user/import_test.exs
+++ b/test/pleroma/user/import_test.exs
@@ -3,7 +3,6 @@
 # SPDX-License-Identifier: AGPL-3.0-only
 
 defmodule Pleroma.User.ImportTest do
-  alias Pleroma.Repo
   alias Pleroma.Tests.ObanHelpers
   alias Pleroma.User
 
diff --git a/test/pleroma/user_search_test.exs b/test/pleroma/user_search_test.exs
index 1deab6888..1af9a1493 100644
--- a/test/pleroma/user_search_test.exs
+++ b/test/pleroma/user_search_test.exs
@@ -3,7 +3,6 @@
 # SPDX-License-Identifier: AGPL-3.0-only
 
 defmodule Pleroma.UserSearchTest do
-  alias Pleroma.Repo
   alias Pleroma.User
   use Pleroma.DataCase
 
diff --git a/test/pleroma/web/activity_pub/transmogrifier/emoji_react_handling_test.exs b/test/pleroma/web/activity_pub/transmogrifier/emoji_react_handling_test.exs
index 9d99df27c..83bf59c6f 100644
--- a/test/pleroma/web/activity_pub/transmogrifier/emoji_react_handling_test.exs
+++ b/test/pleroma/web/activity_pub/transmogrifier/emoji_react_handling_test.exs
@@ -65,7 +65,7 @@ test "it works for incoming unqualified emoji reactions" do
     object = Object.get_by_ap_id(data["object"])
 
     assert object.data["reaction_count"] == 1
-    assert match?([[emoji, _]], object.data["reactions"])
+    assert match?([[^emoji, _]], object.data["reactions"])
   end
 
   test "it reject invalid emoji reactions" do
diff --git a/test/pleroma/web/mastodon_api/update_credentials_test.exs b/test/pleroma/web/mastodon_api/update_credentials_test.exs
index d5fac7e25..d4004bcb6 100644
--- a/test/pleroma/web/mastodon_api/update_credentials_test.exs
+++ b/test/pleroma/web/mastodon_api/update_credentials_test.exs
@@ -375,7 +375,9 @@ test "updates the user's background, upload_limit, returns a HTTP 413", %{
           "pleroma_background_image" => new_background_oversized
         })
 
-      assert user_response = json_response_and_validate_schema(res, 413)
+      assert %{"error" => "File is too large"} == json_response_and_validate_schema(res, 413)
+
+      user = Repo.get(User, user.id)
       assert user.background == %{}
 
       clear_config([:instance, :upload_limit], upload_limit)
diff --git a/test/test_helper.exs b/test/test_helper.exs
index 60a61484f..046517b28 100644
--- a/test/test_helper.exs
+++ b/test/test_helper.exs
@@ -1,6 +1,7 @@
 # Pleroma: A lightweight social networking server
 # Copyright © 2017-2022 Pleroma Authors <https://pleroma.social/>
 # SPDX-License-Identifier: AGPL-3.0-only
+Code.put_compiler_option(:warnings_as_errors, true)
 
 os_exclude = if :os.type() == {:unix, :darwin}, do: [skip_on_mac: true], else: []
 ExUnit.start(exclude: [:federated, :erratic] ++ os_exclude)