Hide number sign for string prefixed external issues

app/models/external_issue.rb

@@ -34,15 +34,13 @@ class ExternalIssue
     %r{(?<issue>\b([A-Z][A-Z0-9_]+-)\d+)}
   end
 
-  def self.reference_prefix
-    '#'
-  end
-
   def to_reference(_from_project = nil)
     id
   end
 
   def reference_link_text(from_project = nil)
-    "#{self.class.reference_prefix}#{id}"
+    return "##{id}" if /^\d+$/.match(id)
+
+    id
   end
 end

spec/models/external_issue_spec.rb

@@ -38,8 +38,17 @@ describe ExternalIssue, models: true do
   end
 
   describe '#reference_link_text' do
-    it 'returns a String reference to the object' do
-      expect(issue.reference_link_text).to eq '#EXT-1234'
+    context 'if issue id has a prefix' do
+      it 'returns the issue ID' do
+        expect(issue.reference_link_text).to eq 'EXT-1234'
+      end
+    end
+
+    context 'if issue id is a number' do
+      let(:issue)   { described_class.new('1234', project) }
+      it 'returns the issue ID prefixed by #' do
+        expect(issue.reference_link_text).to eq '#1234'
+      end
     end
   end
 end