Even with the simplicity of yml configuration that is trending now-a-days, there aren't many sites and documentations that can help us configure rspec pipelines with as ease as configuring jenkins or gitlab.

Below is the sample file that I used for achieving the same.
You can find it over here as well.

image: absk1317/ruby-node-pg:2.6
pipelines:
  default:
    - parallel:
      - step:
          name: Test
          caches:
            - bundler
          script:
            - cp .env.example .env
            - export DATABASE_URL=postgresql://postgres:root@localhost/test_db
            - bundle install -j 4 --path vendor
            - bundle exec rake db:migrate --trace RAILS_ENV=test
            - bundle exec rspec
          services:
            - postgres
      - step:
          name: Lint
          caches:
            - bundler
          script:
            - sed '$d' Gemfile.lock | sed '$d' | sed '$d' > Gemfile.temp_lock && mv Gemfile.temp_lock Gemfile.lock
            - bundle install --path vendor
            - bundle exec pronto run -f bitbucket_pr -c origin/master

definitions:
  caches:
    bundler: ./vendor
  services:
    postgres:
      image: postgres:9.5
      environment:
        POSTGRES_DB: test_db
        POSTGRES_USER: postgres
        POSTGRES_PASSWORD: root

I'm not going in much details here, as it looks quite straight forward. However will add proper comments later on.