Coverage Docs callout for filtering to mirror local results

Problem

There are times when I run my coverage job locally and on gitlab.com and get different results. There is a known workaround to resolve this (make sure you're filtering the same items) but that isn't documented in GitLab docs.

Proposal

Update the locations below to include a tip about how to make coverage match locally / on gitlab.com

• https://docs.gitlab.com/ee/ci/yaml/#coverage
• https://docs.gitlab.com/ee/user/project/pipelines/settings.html#test-coverage-parsing

The original writeup from a user

Hi everyone! I have a little discrepancy with specs coverage in my Rails project. Locally rspec return an information that coverage is about 98%:

Finished in 0.72853 seconds (files took 1.65 seconds to load)

28 examples, 0 failures

Coverage report generated for RSpec to /home/user/projects/app/coverage. 222 / 225 LOC (98.67%) covered.

but on Gitlab I get this result 48%:

Finished in 1.03 seconds (files took 6.18 seconds to load)

28 examples, 0 failures

Coverage report generated for RSpec to /builds/username/app/coverage. 51991 / 106919 LOC (48.63%) covered.

Where is the difference from?

My .gitlab-ci.yml:

image: "ruby:2.5.1"

cache:
  paths:
    - vendor/ruby

before_script:
  - apt-get update -qq && apt-get install -y -qq sqlite3 libsqlite3-dev nodejs
  - ruby -v
  - which ruby
  - gem install bundler --no-ri --no-rdoc
  - bundle install --jobs $(nproc) --path vendor

rspec:
  script:
    - bundle exec rspec