<The Problem
pod install can take some time to complete, and if you have your Pods directory cached - sometimes you don't need to run it again for the current CI run.
This is the problem that the Square team addressed with the plugin CocoaPods Check.
<The answer
CocoaPods Check adds a command pod check, which will return with an error code of not zero if you need to run pod install. This means that you can run:
bundle exec pod check || bundle exec pod install
In your CI instead of just bundle exec pod install and you will get faster CI builds.
To find out more, check out square/cocoapods-check.