BulkImports: Remove epics author finding duplication

Mapping users/author of imported relations is a recurrent work to be
done. Therefore, the
BulkImports::Common::Transformers::UserReferenceTransformer was created
to centralized how it's done.

This commit adds the
BulkImports::Common::Transformers::UserReferenceTransformer as a
transformer in
EE::BulkImports::Groups::Pipelines::EpicsPipeline and removes the
duplicated logic from the
EE::BulkImports::Groups::Transformers::EpicAttributesTransformer

ee/lib/ee/bulk_imports/groups/pipelines/epics_pipeline.rb

@@ -11,6 +11,8 @@ module EE
             query: EE::BulkImports::Groups::Graphql::GetEpicsQuery
 
           transformer ::BulkImports::Common::Transformers::ProhibitedAttributesTransformer
+          transformer ::BulkImports::Common::Transformers::UserReferenceTransformer,
+            reference: :author
           transformer EE::BulkImports::Groups::Transformers::EpicAttributesTransformer
 
           def transform(_, data)

ee/lib/ee/bulk_imports/groups/transformers/epic_attributes_transformer.rb

@@ -7,7 +7,6 @@ module EE
         class EpicAttributesTransformer
           def transform(context, data)
             data
-              .then { |data| add_author_id(context, data) }
               .then { |data| add_parent(context, data) }
               .then { |data| add_children(context, data) }
               .then { |data| add_labels(context, data) }
@@ -15,21 +14,6 @@ module EE
 
           private
 
-          def add_author_id(context, data)
-            user = find_user_by_email(context, data.dig('author', 'public_email'))
-            author_id = user&.id || context.current_user.id
-
-            data
-              .merge('author_id' => author_id)
-              .except('author')
-          end
-
-          def find_user_by_email(context, email)
-            return if email.blank?
-
-            context.group.users.find_by_any_email(email, confirmed: true)
-          end
-
           def add_parent(context, data)
             data.merge(
               'parent' => context.group.epics.find_by_iid(data.dig('parent', 'iid'))

ee/spec/lib/ee/bulk_imports/groups/pipelines/epics_pipeline_spec.rb

@@ -125,6 +125,7 @@ RSpec.describe EE::BulkImports::Groups::Pipelines::EpicsPipeline, :clean_gitlab_
       expect(described_class.transformers)
         .to contain_exactly(
           { klass: BulkImports::Common::Transformers::ProhibitedAttributesTransformer, options: nil },
+          { klass: BulkImports::Common::Transformers::UserReferenceTransformer, options: { reference: :author } },
           { klass: EE::BulkImports::Groups::Transformers::EpicAttributesTransformer, options: nil }
         )
     end

ee/spec/lib/ee/bulk_imports/groups/transformers/epic_attributes_transformer_spec.rb

@@ -27,7 +27,6 @@ RSpec.describe EE::BulkImports::Groups::Transformers::EpicAttributesTransformer
         'due_date_is_fixed' => false,
         'relative_position' => 1073716855,
         'confidential' => false,
-        'author_id' => importer_user.id,
         'parent' => nil,
         'children' => [],
         'labels' => []
@@ -67,57 +66,6 @@ RSpec.describe EE::BulkImports::Groups::Transformers::EpicAttributesTransformer
       end
     end
 
-    context 'epic author' do
-      it 'finds user by primary confirmed email' do
-        member_user = create(:user, email: 'member@email.com')
-        group.add_owner(member_user)
-
-        data = epic_data(public_email: member_user.email)
-
-        transformed_data = subject.transform(context, data)
-
-        expect(transformed_data['author_id']).to eq(member_user.id)
-      end
-
-      it 'falls back to the importer user if primary email is not confirmed' do
-        member_user = create(:user, :unconfirmed, email: 'member@email.com')
-
-        group.add_owner(member_user)
-
-        data = epic_data(public_email: member_user.email)
-
-        transformed_data = subject.transform(context, data)
-
-        expect(transformed_data['author_id']).to eq(importer_user.id)
-      end
-
-      it 'findes user by secondary confirmed email' do
-        secondary_email = 'other@email.com'
-        member_user = create(:user, email: 'member@email.com')
-        create(:email, :confirmed, user: member_user, email: secondary_email)
-        group.add_owner(member_user)
-
-        data = epic_data(public_email: secondary_email)
-
-        transformed_data = subject.transform(context, data)
-
-        expect(transformed_data['author_id']).to eq(member_user.id)
-      end
-
-      it 'falls back to the importer user if secondary email is not confirmed' do
-        secondary_email = 'other@email.com'
-        member_user = create(:user, email: 'member@email.com')
-        create(:email, user: member_user, email: secondary_email)
-        group.add_owner(member_user)
-
-        data = epic_data(public_email: secondary_email)
-
-        transformed_data = subject.transform(context, data)
-
-        expect(transformed_data['author_id']).to eq(importer_user.id)
-      end
-    end
-
     def epic_data(parent_iid: nil, children_iids: [], labels_titles: [], public_email: '')
       {
         'title' => 'title',
@@ -132,9 +80,6 @@ RSpec.describe EE::BulkImports::Groups::Transformers::EpicAttributesTransformer
         'due_date_is_fixed' => false,
         'relative_position' => 1073716855,
         'confidential' => false,
-        'author' => {
-          'public_email' => public_email
-        },
         'parent' => {
           'iid' => parent_iid
         },