Monitoring and Testing in Mobile System Design

Let’s start with a scenario: a popular health tracking app released a minor update. The app was crashing silently after login on older Android or iOS devices, causing a cascade of issues: unsynced fitness data, broken wearable integrations, and frustrated users abandoning the platform. Within a few days, it faced a surge of 1-star reviews. By the time engineers found the root cause, thousands of users had already left.

This isn’t uncommon. Mobile apps run on fragmented ecosystems, hundreds of device models, OS versions, and real-world conditions. Without proactive monitoring, even a small bug can go undetected until it causes real damage.

Monitoring is more than error tracking. It’s about building systems that can observe themselves in production: detecting performance bottlenecks, identifying crash patterns, and capturing user behavior to drive better decisions. Without it, even well-tested systems can collapse in the hands of real users.

This lesson explores how monitoring, paired with thorough testing, ensures that mobile systems remain stable, resilient, and user-friendly long after deployment.

Let’s start with understanding the testing strategies in mobile apps.

Testing strategies in mobile System Design

Testing in mobile systems is about enforcing architectural discipline, ensuring reliability across fragmented environments, and supporting safe iteration at scale. Mobile apps must gracefully handle diverse OS versions, hardware limitations, and inconsistent network conditions. Without well-defined testing strategies, even small updates can destabilize the user experience across millions of devices.

Robust testing allows developers to validate components in isolation, simulate user journeys, stress systems under edge cases, and protect user trust through secure, compliant implementations.

Let’s explore different strategies for testing a mobile app.

Unit and integration testing

In mobile System Design, unit and integration tests form the safety net that allows teams to build, refactor, and release confidently.

• Unit testing: Unit testing focuses on verifying individual components in isolation. For mobile apps, this often means testing:

  • ViewModels or Presenters (in MVVM or MVP).

  • Business logic in use cases or interactors.

  • Utility functions, formatters, and validation logic.

By structuring our app around clean architecture or similar separation-of-concerns patterns, we make core functionality testable without depending on UI frameworks or databases. The following table highlights some common tools for both Android and iOS to unit test the apps:

These tools allow mocking of dependencies, like repositories or network services, to ensure logic is deterministic and fast.

• Integration testing: Where unit tests ensure correctness in isolation, integration tests validate how components work together. This can include:

  • Verifying data flows between local databases (Room, Core Data) and business logic.

  • Testing service calls and data mapping with fake servers or mock APIs.

  • Ensuring DI frameworks (like Hilt or Koin) inject dependencies properly.

Integration tests ...