Improve uniqueness validation error message

app/models/related_issue.rb

@@ -2,6 +2,7 @@ class RelatedIssue < ActiveRecord::Base
   belongs_to :issue
   belongs_to :related_issue, class_name: 'Issue'
 
-  validates :issue, presence: true, uniqueness: { scope: :related_issue_id }
+  validates :issue, presence: true
   validates :related_issue, presence: true
+  validates :issue, uniqueness: { scope: :related_issue_id, message: 'is already related' }
 end

spec/models/related_issue_spec.rb

@@ -11,6 +11,20 @@ describe RelatedIssue do
 
     it { is_expected.to validate_presence_of(:issue) }
     it { is_expected.to validate_presence_of(:related_issue) }
-    it { is_expected.to validate_uniqueness_of(:issue).scoped_to(:related_issue_id) }
+    it do
+      is_expected.to validate_uniqueness_of(:issue)
+        .scoped_to(:related_issue_id)
+        .with_message(/already related/)
+    end
+
+    context 'self relation' do
+      it 'invalidates object' do
+        issue = create :issue
+        related_issue = build :related_issue, issue: issue, related_issue: issue
+
+        expect(related_issue).to be_invalid
+        expect(related_issue.errors[:issue]).to include("cannot be related to itself")
+      end
+    end
   end
 end

spec/services/related_issues/create_service_spec.rb

@@ -136,7 +136,7 @@ describe RelatedIssues::CreateService, service: true do
       end
 
       it 'returns error' do
-        is_expected.to eq(message: "Validation failed: Issue has already been taken", status: :error, http_status: 401)
+        is_expected.to eq(message: "Validation failed: Issue is already related", status: :error, http_status: 401)
       end
 
       it 'no relation is created' do