Prevent default overwrite for theme and color ID in user API

changelogs/unreleased/fix-prevent-user-theme-color-api-overwrite.yml

+---
+title: Prevent default overwrite for theme and color ID in user API
+merge_request: 26792
+author: Fabio Huser
+type: fixed

lib/api/users.rb

@@ -52,8 +52,8 @@ module API
           optional :external, type: Boolean, desc: 'Flag indicating the user is an external user'
           # TODO: remove rubocop disable - https://gitlab.com/gitlab-org/gitlab/issues/14960
           optional :avatar, type: File, desc: 'Avatar image for user' # rubocop:disable Scalability/FileUploads
-          optional :theme_id, type: Integer, default: 1, desc: 'The GitLab theme for the user'
-          optional :color_scheme_id, type: Integer, default: 1, desc: 'The color scheme for the file viewer'
+          optional :theme_id, type: Integer, desc: 'The GitLab theme for the user'
+          optional :color_scheme_id, type: Integer, desc: 'The color scheme for the file viewer'
           optional :private_profile, type: Boolean, desc: 'Flag indicating the user has a private profile'
           all_or_none_of :extern_uid, :provider
 

spec/requests/api/users_spec.rb

@@ -832,6 +832,13 @@ describe API::Users, :do_not_mock_admin_mode do
       expect(user.reload.private_profile).to eq(false)
     end
 
+    it "does have default values for theme and color-scheme ID" do
+      put api("/users/#{user.id}", admin), params: {}
+
+      expect(user.reload.theme_id).to eq(Gitlab::Themes.default.id)
+      expect(user.reload.color_scheme_id).to eq(Gitlab::ColorSchemes.default.id)
+    end
+
     it "updates private profile" do
       put api("/users/#{user.id}", admin), params: { private_profile: true }
 
@@ -857,6 +864,19 @@ describe API::Users, :do_not_mock_admin_mode do
       expect(user.reload.private_profile).to eq(true)
     end
 
+    it "does not modify theme or color-scheme ID when field is not provided" do
+      theme = Gitlab::Themes.each.find { |t| t.id != Gitlab::Themes.default.id }
+      scheme = Gitlab::ColorSchemes.each.find { |t| t.id != Gitlab::ColorSchemes.default.id }
+
+      user.update(theme_id: theme.id, color_scheme_id: scheme.id)
+
+      put api("/users/#{user.id}", admin), params: {}
+
+      expect(response).to have_gitlab_http_status(:ok)
+      expect(user.reload.theme_id).to eq(theme.id)
+      expect(user.reload.color_scheme_id).to eq(scheme.id)
+    end
+
     it "does not update admin status" do
       put api("/users/#{admin_user.id}", admin), params: { can_create_group: false }