How to avoid angular to rebuild all the modules when running ng test?

I am using a Jenkins pipeline to build my angular 4 application. I am using angular-cli ng build -prod and ng test to run the tests. The tests' step is extremely slow, taking more time then the build itself. I found out that this was happening because during this step all the modules are rebuilt despite the build had just finished. Isn't there a way to avoid the rebuild during the tests' phase since the modules were already built?