1 files changed, 109 insertions, 0 deletions
diff --git a/spec/helpers/lazy_image_tag_helper_spec.rb b/spec/helpers/lazy_image_tag_helper_spec.rb
new file mode 100644
index 00000000000..2d9445bb6cb
--- /dev/null
+++ b/spec/helpers/lazy_image_tag_helper_spec.rb
@@ -0,0 +1,109 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe LazyImageTagHelper do
+  describe '#image_tag' do
+    let(:image_src) { '/path/to/image.jpg' }
+    let(:dark_image_src) { '/path/to/image_dark.jpg' }
+
+    context 'when only source passed' do
+      let(:current_user) { create(:user) }
+      let(:result) { image_tag(image_src) }
+
+      it 'returns a lazy image tag by default' do
+        expect(result).to eq(
+          "<img data-src=\"#{image_src}\" class=\"lazy\" src=\"#{placeholder_image}\" />"
+        )
+      end
+    end
+
+    context 'when lazy mode is disabled' do
+      let(:current_user) { create(:user) }
+      let(:result) { image_tag(image_src, lazy: false) }
+
+      it 'returns a normal image tag' do
+        expect(result).to eq(
+          "<img src=\"#{image_src}\" />"
+        )
+      end
+    end
+
+    context 'when Dark Mode is enabled' do
+      let(:current_user) { create(:user, theme_id: 11) }
+
+      context 'when auto dark enabled' do
+        let(:result) { image_tag(image_src, auto_dark: true) }
+
+        it 'adds an auto dark mode class from gitlab-ui' do
+          expect(result).to eq(
+            "<img class=\"gl-dark-invert-keep-hue lazy\" data-src=\"#{image_src}\" src=\"#{placeholder_image}\" />"
+          )
+        end
+      end
+
+      context 'when auto dark disabled' do
+        let(:result) { image_tag(image_src, auto_dark: false) }
+
+        it 'does nothing' do
+          expect(result).to eq(
+            "<img data-src=\"#{image_src}\" class=\"lazy\" src=\"#{placeholder_image}\" />"
+          )
+        end
+      end
+
+      context 'when dark variant is present' do
+        let(:result) { image_tag(image_src, dark_variant: dark_image_src) }
+
+        it 'uses dark variant as a source' do
+          expect(result).to eq(
+            "<img data-src=\"#{dark_image_src}\" class=\"lazy\" src=\"#{placeholder_image}\" />"
+          )
+        end
+      end
+    end
+
+    context 'when Dark Mode is disabled' do
+      let(:current_user) { create(:user, theme_id: 1) }
+
+      context 'when auto dark enabled' do
+        let(:result) { image_tag(image_src, auto_dark: true) }
+
+        it 'does not add a dark mode class from gitlab-ui' do
+          expect(result).to eq(
+            "<img data-src=\"#{image_src}\" class=\"lazy\" src=\"#{placeholder_image}\" />"
+          )
+        end
+      end
+
+      context 'when auto dark disabled' do
+        let(:result) { image_tag(image_src, auto_dark: true) }
+
+        it 'does nothing' do
+          expect(result).to eq(
+            "<img data-src=\"#{image_src}\" class=\"lazy\" src=\"#{placeholder_image}\" />"
+          )
+        end
+      end
+
+      context 'when dark variant is present' do
+        let(:result) { image_tag(image_src, dark_variant: dark_image_src) }
+
+        it 'uses original image as a source' do
+          expect(result).to eq(
+            "<img data-src=\"#{image_src}\" class=\"lazy\" src=\"#{placeholder_image}\" />"
+          )
+        end
+      end
+    end
+
+    context 'when auto_dark and dark_variant are both passed' do
+      let(:current_user) { create(:user) }
+
+      it 'does not add a dark mode class from gitlab-ui' do
+        expect { image_tag('image.jpg', dark_variant: 'image_dark.jpg', auto_dark: true) }
+          .to raise_error(ArgumentError, 'dark_variant and auto_dark are mutually exclusive')
+      end
+    end
+  end
+end