Render titles with source links for TIMDEX records

Why these changes are being introduced:

In TIMDEX UI, titles linked to full record views. That feature is not
currently implemented in USE UI.

Relevant ticket(s):

* [USE-99](https://mitlibraries.atlassian.net/browse/USE-99)

How this addresses that need:

This updates TIMDEX title links to use the `source_link` field.

Side effects of this change:

When developing TIMDEX UI, we decided not to test any view logic. I've
moved the logic in this change to the Search Helper in order to test it,
but we may want to discuss whether to revisit integration testing in
USE UI.

Author: jazairi

app/helpers/search_helper.rb

@@ -14,6 +14,14 @@ def format_highlight_label(field_name)
     field_name.underscore.humanize
   end
 
+  def link_to_result(result)
+    if result['source_link'].present?
+      link_to(result['title'], result['source_link'])
+    else
+      result['title']
+    end
+  end
+
   def view_online(result)
     return unless result['source_link'].present?
 

app/views/search/_result.html.erb

@@ -1,7 +1,8 @@
 <li class="result">
   <div class="result-content">
     <h3 class="record-title">
-      <span class="sr">Title: </span><%= link_to(result['title'], record_path(result['identifier'])) %>
+      <span class="sr">Title: </span>
+      <%= link_to_result(result) %>
     </h3>
 
     <p class="pub-info">

test/helpers/search_helper_test.rb

@@ -171,4 +171,36 @@ def setup
     }
     assert_equal ['Authors: person, sample'], applied_advanced_terms(query)
   end
+
+  test 'link_to_result returns link when source_link is present' do
+    result = {
+      'title' => 'Sample Document Title',
+      'source_link' => 'https://example.com/document'
+    }
+    expected_link = '<a href="https://example.com/document">Sample Document Title</a>'
+    assert_equal expected_link, link_to_result(result)
+  end
+
+  test 'link_to_result returns plain title when source_link is nil' do
+    result = {
+      'title' => 'Sample Document Title',
+      'source_link' => nil
+    }
+    assert_equal 'Sample Document Title', link_to_result(result)
+  end
+
+  test 'link_to_result returns plain title when source_link is empty string' do
+    result = {
+      'title' => 'Sample Document Title',
+      'source_link' => ''
+    }
+    assert_equal 'Sample Document Title', link_to_result(result)
+  end
+
+  test 'link_to_result returns plain title when source_link key is absent' do
+    result = {
+      'title' => 'Sample Document Title'
+    }
+    assert_equal 'Sample Document Title', link_to_result(result)
+  end
 end