Resolve "GitLab Community Edition 10.5.3 shows plural for 1 item"

app/views/projects/diffs/_stats.html.haml

@@ -7,9 +7,9 @@
     = icon("caret-down", class: "prepend-left-5")
   %span.diff-stats-additions-deletions-expanded#diff-stats
     with
-    %strong.cgreen #{sum_added_lines} additions
+    %strong.cgreen= pluralize(sum_added_lines, 'addition')
     and
-    %strong.cred #{sum_removed_lines} deletions
+    %strong.cred= pluralize(sum_removed_lines, 'deletion')
   .diff-stats-additions-deletions-collapsed.pull-right.hidden-xs.hidden-sm{ "aria-hidden": "true", "aria-describedby": "diff-stats" }
     %strong.cgreen<
       +#{sum_added_lines}

changelogs/unreleased/44022-singular-1-diff.yml

+---
+title: Use singular in the diff stats if only one line has been changed
+merge_request: 17697
+author: Jan Beckmann
+type: fixed

spec/views/projects/diffs/_stats.html.haml_spec.rb

+require 'spec_helper'
+
+describe 'projects/diffs/_stats.html.haml' do
+  let(:project) { create(:project, :repository) }
+  let(:commit) { project.commit('570e7b2abdd848b95f2f578043fc23bd6f6fd24d') }
+
+  def render_view
+    render partial: "projects/diffs/stats", locals: { diff_files: commit.diffs.diff_files }
+  end
+
+  context 'when the commit contains several changes' do
+    it 'uses plural for additions' do
+      render_view
+
+      expect(rendered).to have_text('additions')
+    end
+
+    it 'uses plural for deletions' do
+      render_view
+    end
+  end
+
+  context 'when the commit contains no addition and no deletions' do
+    let(:commit) { project.commit('4cd80ccab63c82b4bad16faa5193fbd2aa06df40') }
+
+    it 'uses plural for additions' do
+      render_view
+
+      expect(rendered).to have_text('additions')
+    end
+
+    it 'uses plural for deletions' do
+      render_view
+
+      expect(rendered).to have_text('deletions')
+    end
+  end
+
+  context 'when the commit contains exactly one addition and one deletion' do
+    let(:commit) { project.commit('08f22f255f082689c0d7d39d19205085311542bc') }
+
+    it 'uses singular for additions' do
+      render_view
+
+      expect(rendered).to have_text('addition')
+      expect(rendered).not_to have_text('additions')
+    end
+
+    it 'uses singular for deletions' do
+      render_view
+
+      expect(rendered).to have_text('deletion')
+      expect(rendered).not_to have_text('deletions')
+    end
+  end
+end