diff --git a/lib/gitlab/ci/variables/collection.rb b/lib/gitlab/ci/variables/collection.rb
index 97ca6dc3d3d..ae7415fcdb1 100644
--- a/lib/gitlab/ci/variables/collection.rb
+++ b/lib/gitlab/ci/variables/collection.rb
@@ -14,7 +14,6 @@ module Gitlab
           @variables.append(Collection::Item.fabricate(resource))
         end
 
-        # TODO, specs
         def concat(resources)
           resources.each { |variable| self.append(variable) }
         end
diff --git a/spec/lib/gitlab/ci/variables/collection/item_spec.rb b/spec/lib/gitlab/ci/variables/collection/item_spec.rb
index 6f86d658f52..37394c3e80f 100644
--- a/spec/lib/gitlab/ci/variables/collection/item_spec.rb
+++ b/spec/lib/gitlab/ci/variables/collection/item_spec.rb
@@ -39,6 +39,14 @@ describe Gitlab::Ci::Variables::Collection::Item do
     end
   end
 
+  describe '#[]' do
+    it 'behaves like a hash accessor' do
+      item = described_class.new(**variable)
+
+      expect(item[:key]).to eq 'VAR'
+    end
+  end
+
   describe '#to_hash' do
     it 'returns a hash representation of a collection item' do
       expect(described_class.new(**variable).to_hash).to eq variable
diff --git a/spec/lib/gitlab/ci/variables/collection_spec.rb b/spec/lib/gitlab/ci/variables/collection_spec.rb
index 9ee39d40625..005e2bb17b4 100644
--- a/spec/lib/gitlab/ci/variables/collection_spec.rb
+++ b/spec/lib/gitlab/ci/variables/collection_spec.rb
@@ -37,6 +37,31 @@ describe Gitlab::Ci::Variables::Collection do
     end
   end
 
+  describe '#concat' do
+    it 'appends all elements from an array' do
+      collection = described_class.new([{ key: 'VAR_1', value: '1' }])
+      variables = [{ key: 'VAR_2', value: '2' }, { key: 'VAR_3', value: '3' }]
+
+      collection.concat(variables)
+
+      expect(collection).to include(key: 'VAR_1', value: '1', public: true)
+      expect(collection).to include(key: 'VAR_2', value: '2', public: true)
+      expect(collection).to include(key: 'VAR_3', value: '3', public: true)
+    end
+
+    it 'appends all elements from other collection' do
+      collection = described_class.new([{ key: 'VAR_1', value: '1' }])
+      additional = described_class.new([{ key: 'VAR_2', value: '2' },
+                                        { key: 'VAR_3', value: '3' }])
+
+      collection.concat(additional)
+
+      expect(collection).to include(key: 'VAR_1', value: '1', public: true)
+      expect(collection).to include(key: 'VAR_2', value: '2', public: true)
+      expect(collection).to include(key: 'VAR_3', value: '3', public: true)
+    end
+  end
+
   describe '#+' do
     it 'makes it possible to combine with an array' do
       collection = described_class.new([{ key: 'TEST', value: 1 }])