Add a test

updater/spec/dependabot/updater/operations/refresh_group_update_pull_request_spec.rb

@@ -231,4 +231,18 @@
       group_update_all.perform
     end
   end
+
+  describe "#deduce_updated_dependency" do
+    it "returns nil if dependency is nil" do
+      dependency = nil
+      original_dependency = dependency_snapshot.dependencies.first
+      expect(group_update_all.deduce_updated_dependency(dependency, original_dependency)).to eq(nil)
+    end
+
+    it "returns nil if original_dependency is nil" do
+      dependency = dependency_snapshot.dependencies.first
+      original_dependency = nil
+      expect(group_update_all.deduce_updated_dependency(dependency, original_dependency)).to eq(nil)
+    end
+  end
 end