diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 11e97ca81..89d52a61d 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -81,7 +81,8 @@ jobs:
       - name: Install build dependancies
         # - fonts pickable by ImageMagick
         # - rust for YJIT support
-        run: sudo apt-get update && sudo apt-get install -y gsfonts rustc redis-server
+        # - poppler-utils for pdf previews
+        run: sudo apt-get update && sudo apt-get install -y gsfonts rustc redis-server poppler-utils
 
       - name: Setup the app runtime and dependencies
         uses: ./.github/actions/ci-setup-rails
diff --git a/spec/helpers/gallery_helper_spec.rb b/spec/helpers/gallery_helper_spec.rb
new file mode 100644
index 000000000..41469798c
--- /dev/null
+++ b/spec/helpers/gallery_helper_spec.rb
@@ -0,0 +1,57 @@
+RSpec.describe GalleryHelper, type: :helper do
+  let(:procedure) { create(:procedure_with_dossiers) }
+  let(:type_de_champ_pj) { create(:type_de_champ_piece_justificative, stable_id: 3, libelle: 'Justificatif de domicile', procedure:) }
+  let(:champ_pj) { create(:champ_piece_justificative, type_de_champ: type_de_champ_pj) }
+  let(:blob_info) do
+    {
+      filename: file.original_filename,
+      byte_size: file.size,
+      checksum: Digest::SHA256.file(file.path),
+      content_type: file.content_type,
+      # we don't want to run virus scanner on this file
+      metadata: { virus_scan_result: ActiveStorage::VirusScanner::SAFE }
+    }
+  end
+  let(:blob) do
+    blob = ActiveStorage::Blob.create_before_direct_upload!(**blob_info)
+    blob.upload(file)
+    blob
+  end
+  let(:attachment) { ActiveStorage::Attachment.create(name: "test", blob: blob, record: champ_pj) }
+
+  describe ".variant_url_for" do
+    subject { variant_url_for(attachment) }
+
+    context "when attachment can be represented with a variant" do
+      let(:file) { fixture_file_upload('spec/fixtures/files/logo_test_procedure.png', 'image/png') }
+
+      it { expect { subject }.to change { ActiveStorage::VariantRecord.count }.by(1) }
+      it { is_expected.not_to eq("apercu-indisponible.png") }
+    end
+
+    context "when attachment cannot be represented with a variant" do
+      let(:file) { fixture_file_upload('spec/fixtures/files/instructeurs-file.csv', 'text/csv') }
+
+      it { expect { subject }.not_to change { ActiveStorage::VariantRecord.count } }
+      it { is_expected.to eq("apercu-indisponible.png") }
+    end
+  end
+
+  describe ".preview_url_for" do
+    subject { preview_url_for(attachment) }
+
+    context "when attachment can be represented with a preview" do
+      let(:file) { fixture_file_upload('spec/fixtures/files/RIB.pdf', 'application/pdf') }
+
+      it { expect { subject }.to change { ActiveStorage::VariantRecord.count }.by(1) }
+      it { is_expected.not_to eq("pdf-placeholder.png") }
+    end
+
+    context "when attachment cannot be represented with a preview" do
+      let(:file) { fixture_file_upload('spec/fixtures/files/instructeurs-file.csv', 'text/csv') }
+
+      it { expect { subject }.not_to change { ActiveStorage::VariantRecord.count } }
+      it { is_expected.to eq("pdf-placeholder.png") }
+    end
+  end
+end