1 files changed, 143 insertions, 0 deletions
diff --git a/spec/lib/gitlab/graphql/present/field_extension_spec.rb b/spec/lib/gitlab/graphql/present/field_extension_spec.rb
new file mode 100644
index 00000000000..5e66e16d655
--- /dev/null
+++ b/spec/lib/gitlab/graphql/present/field_extension_spec.rb
@@ -0,0 +1,143 @@
+# frozen_string_literal: true
+require 'spec_helper'
+
+RSpec.describe Gitlab::Graphql::Present::FieldExtension do
+  include GraphqlHelpers
+
+  let_it_be(:user) { create(:user) }
+
+  let(:object) { double(value: 'foo') }
+  let(:owner) { fresh_object_type }
+  let(:field_name) { 'value' }
+  let(:field) do
+    ::Types::BaseField.new(name: field_name, type: GraphQL::STRING_TYPE, null: true, owner: owner)
+  end
+
+  let(:base_presenter) do
+    Class.new(SimpleDelegator) do
+      def initialize(object, **options)
+        super(object)
+        @object = object
+        @options = options
+      end
+    end
+  end
+
+  def resolve_value
+    resolve_field(field, object, current_user: user, object_type: owner)
+  end
+
+  context 'when the object does not declare a presenter' do
+    it 'does not affect normal resolution' do
+      expect(resolve_value).to eq 'foo'
+    end
+  end
+
+  describe 'interactions with inheritance' do
+    def parent
+      type = fresh_object_type('Parent')
+      type.present_using(provide_foo)
+      type.field :foo, ::GraphQL::INT_TYPE, null: true
+      type.field :value, ::GraphQL::STRING_TYPE, null: true
+      type
+    end
+
+    def child
+      type = Class.new(parent)
+      type.graphql_name 'Child'
+      type.present_using(provide_bar)
+      type.field :bar, ::GraphQL::INT_TYPE, null: true
+      type
+    end
+
+    def provide_foo
+      Class.new(base_presenter) do
+        def foo
+          100
+        end
+      end
+    end
+
+    def provide_bar
+      Class.new(base_presenter) do
+        def bar
+          101
+        end
+      end
+    end
+
+    it 'can resolve value, foo and bar' do
+      type = child
+      value = resolve_field(:value, object, object_type: type)
+      foo = resolve_field(:foo, object, object_type: type)
+      bar = resolve_field(:bar, object, object_type: type)
+
+      expect([value, foo, bar]).to eq ['foo', 100, 101]
+    end
+  end
+
+  shared_examples 'calling the presenter method' do
+    it 'calls the presenter method' do
+      expect(resolve_value).to eq presenter.new(object, current_user: user).send(field_name)
+    end
+  end
+
+  context 'when the object declares a presenter' do
+    before do
+      owner.present_using(presenter)
+    end
+
+    context 'when the presenter overrides the original method' do
+      def twice
+        Class.new(base_presenter) do
+          def value
+            @object.value * 2
+          end
+        end
+      end
+
+      let(:presenter) { twice }
+
+      it_behaves_like 'calling the presenter method'
+    end
+
+    # This is exercised here using an explicit `resolve:` proc, but
+    # @resolver_proc values are used in field instrumentation as well.
+    context 'when the field uses a resolve proc' do
+      let(:presenter) { base_presenter }
+      let(:field) do
+        ::Types::BaseField.new(
+          name: field_name,
+          type: GraphQL::STRING_TYPE,
+          null: true,
+          owner: owner,
+          resolve: ->(obj, args, ctx) { 'Hello from a proc' }
+        )
+      end
+
+      specify { expect(resolve_value).to eq 'Hello from a proc' }
+    end
+
+    context 'when the presenter provides a new method' do
+      def presenter
+        Class.new(base_presenter) do
+          def current_username
+            "Hello #{@options[:current_user]&.username} from the presenter!"
+          end
+        end
+      end
+
+      context 'when we select the original field' do
+        it 'is unaffected' do
+          expect(resolve_value).to eq 'foo'
+        end
+      end
+
+      context 'when we select the new field' do
+        let(:field_name) { 'current_username' }
+
+        it_behaves_like 'calling the presenter method'
+      end
+    end
+  end
+end