[EE] Fix unassign slash command preview

app/services/quick_actions/interpret_service.rb

@@ -139,8 +139,10 @@ module QuickActions
         'Remove assignee'
       end
     end
-    explanation do
-      "Removes #{'assignee'.pluralize(issuable.assignees.size)} #{issuable.assignees.map(&:to_reference).to_sentence}."
+    explanation do |users = nil|
+      assignees = issuable.assignees
+      assignees &= users if users.present? && issuable.allows_multiple_assignees?
+      "Removes #{'assignee'.pluralize(assignees.size)} #{assignees.map(&:to_reference).to_sentence}."
     end
     params do
       issuable.allows_multiple_assignees? ? '@user1 @user2' : ''

changelogs/unreleased/4950-unassign-slash-command-preview-fix.yml

+---
+title: Fix unassign slash command preview
+merge_request: 18447
+author:
+type: fixed

ee/spec/services/quick_actions/interpret_service_spec.rb

@@ -4,6 +4,7 @@ describe QuickActions::InterpretService do
   let(:user) { create(:user) }
   let(:developer) { create(:user) }
   let(:developer2) { create(:user) }
+  let(:developer3) { create(:user) }
   let(:project) { create(:project, :public) }
   let(:issue) { create(:issue, project: project) }
   let(:service) { described_class.new(project, developer) }
@@ -115,4 +116,39 @@ describe QuickActions::InterpretService do
       end
     end
   end
+
+  describe '#explain' do
+    describe 'unassign command' do
+      let(:content) { '/unassign' }
+      let(:issue) { create(:issue, project: project, assignees: [developer, developer2]) }
+
+      it "includes all assignees' references" do
+        _, explanations = service.explain(content, issue)
+
+        expect(explanations).to eq(["Removes assignees @#{developer.username} and @#{developer2.username}."])
+      end
+    end
+
+    describe 'unassign command with assignee references' do
+      let(:content) { "/unassign @#{developer.username} @#{developer3.username}" }
+      let(:issue) { create(:issue, project: project, assignees: [developer, developer2, developer3]) }
+
+      it 'includes only selected assignee references' do
+        _, explanations = service.explain(content, issue)
+
+        expect(explanations).to eq(["Removes assignees @#{developer.username} and @#{developer3.username}."])
+      end
+    end
+
+    describe 'unassign command with non-existent assignee reference' do
+      let(:content) { "/unassign @#{developer.username} @#{developer3.username}" }
+      let(:issue) { create(:issue, project: project, assignees: [developer, developer2]) }
+
+      it 'ignores non-existent assignee references' do
+        _, explanations = service.explain(content, issue)
+
+        expect(explanations).to eq(["Removes assignee @#{developer.username}."])
+      end
+    end
+  end
 end