Revamping the Android Testing Pipeline at Dropbox
Article Summary
Dropbox cut their Android CI pipeline from 75 minutes to 25 minutes without switching build systems. Here's how a team of 60+ mobile engineers solved testing at scale.
As Dropbox's Android team grew from 12 to 60+ engineers, their testing pipeline became a productivity killer. Engineers started writing fewer tests and bundling changes into massive PRs to avoid the wait. The Mobile Foundation team rebuilt their entire CI approach using selective testing, Firebase Test Lab, and smart parallelization.
Key Takeaways
- Borrowed AndroidX's Affected Module Detector to run only necessary tests per PR
- Migrated from custom Python tooling to Gradle, Kotlin, Firebase Test Lab, and Jacoco
- Sharded 400 modules across 10 VMs, testing just 2 modules per VM on average
- Reduced worst case compute from 75 minutes to 35 minutes with better parallelization
- Open sourced their AffectedModuleDetector plugin for the Android community
Critical Insight
By testing only affected modules and leveraging cloud infrastructure, Dropbox achieved a 67% reduction in CI time while supporting 3x team growth.
