Change avatar error message to include allowed file formats

app/models/concerns/avatarable.rb

@@ -21,7 +21,7 @@ module Avatarable
   def avatar_type
     unless self.avatar.image?
-      self.errors.add :avatar, "only images allowed"
+      errors.add :avatar, "file format is not supported. Please try one of the following supported formats: #{AvatarUploader::IMAGE_EXT.join(', ')}"
     end
   end

app/models/group.rb

@@ -189,12 +189,6 @@ class Group < Namespace
     owners.include?(user) && owners.size == 1
   end
-  def avatar_type
-    unless self.avatar.image?
-      self.errors.add :avatar, "only images allowed"
-    end
-  end
-
   def post_create_hook
     Gitlab::AppLogger.info("Group \"#{name}\" was created")

changelogs/unreleased/43771-improve-avatar-error-message.yml

+---
+title: Change avatar error message to include allowed file formats
+merge_request: 17747
+author: Fabian Schneider
+type: changed

spec/models/group_spec.rb

@@ -240,7 +240,7 @@ describe Group do
     it "is false if avatar is html page" do
       group.update_attribute(:avatar, 'uploads/avatar.html')
-      expect(group.avatar_type).to eq(["only images allowed"])
+      expect(group.avatar_type).to eq(["file format is not supported. Please try one of the following supported formats: png, jpg, jpeg, gif, bmp, tiff"])
     end
   end

spec/models/project_spec.rb

@@ -922,7 +922,7 @@ describe Project do
     it 'is false if avatar is html page' do
       project.update_attribute(:avatar, 'uploads/avatar.html')
-      expect(project.avatar_type).to eq(['only images allowed'])
+      expect(project.avatar_type).to eq(['file format is not supported. Please try one of the following supported formats: png, jpg, jpeg, gif, bmp, tiff'])
     end
   end

spec/models/user_spec.rb

@@ -1222,7 +1222,7 @@ describe User do
     it 'is false if avatar is html page' do
       user.update_attribute(:avatar, 'uploads/avatar.html')
-      expect(user.avatar_type).to eq(['only images allowed'])
+      expect(user.avatar_type).to eq(['file format is not supported. Please try one of the following supported formats: png, jpg, jpeg, gif, bmp, tiff'])
     end
   end