How to Fix Unreliable Tests: A Guide for Software Engineers

Unreliable tests make the team lose confidence in the automated pipelines. Understanding causes of flakiness and how to fix them will bring confidence back.

In the world of software development, testing is a crucial part of ensuring the quality and reliability of your code. However, one common challenge that software engineers often face is dealing with unreliable tests. Unreliable tests can be frustrating and time-consuming. In this blog, we’ll explore the common causes of unreliable tests and provide practical strategies to fix them.

Understanding the Causes of Unreliable Tests

Before we dive into solutions, it’s essential to understand the underlying causes of unreliable tests. By identifying the root issues, you can better target your efforts to fix them. [1]

  1. Flakiness due to Race Conditions: One of the most common causes of unreliable tests is race conditions. These occur when multiple processes or threads are competing for resources simultaneously, leading to unpredictable outcomes.
  2. Dependence on External Factors: Tests that rely on external dependencies, such as databases, APIs, or third-party services, can become unreliable if these factors change unexpectedly.
  3. Inadequate Test Data Management: If your tests don’t manage test data properly or if they leave behind stateful artifacts, they can lead to unreliability over time.
  4. Fragile Tests: Tests that are overly sensitive to changes in the code under test can break frequently, even with minor updates.

Strategies for Fixing Unreliable Tests

Now that we’ve identified the root causes, let’s explore strategies to fix unreliable tests:

Mitigate Race Conditions

To address race conditions, consider the following approaches:

  • Use Locking Mechanisms: Employ mutex’es, semaphores, or other locking mechanisms to ensure that critical sections of your code are accessed by only one thread at a time.
  • Threading Strategies: Employ thread-safe practices and techniques, such as thread synchronization, to minimize the occurrence of race conditions.

Isolate External Dependencies

To reduce reliance on external factors, consider the following methods:

  • Mocking and Stubbing: Use mock objects or stubs to simulate the behavior of external dependencies. Furthermore, this allows you to control and isolate their behavior during testing.
  • Containerization: Use containers like Docker to create a reproducible and isolated testing environment that includes all required external dependencies.

Effective Test Data Management

Proper test data management is vital for test reliability. Here are some key steps to follow:

  • Data Cleanup: Ensure your tests clean up after themselves by removing any test data or state changes created during the test run.
  • Data Seeding: Implement data seeding mechanisms to ensure that your tests have consistent and known starting points.

Stabilize Fragile Tests

Fragile tests can be a headache, but these practices can help stabilize them:

  • Looser Assertions: Instead of asserting every detail of the output, focus on the essential aspects of the test’s behavior. This can make tests more resilient to minor code changes.
  • Use Page Objects: For UI tests, use the Page Object pattern to encapsulate the UI elements and their behavior. As a result, this abstracts the test code from UI changes and makes tests more stable.

Regular Maintenance and Continuous Integration

Fixing unreliable tests is just the beginning. To maintain their reliability over time, consider integrating these practices:

  • Continuous Integration (CI): Implement a robust CI pipeline that runs your tests automatically whenever code changes are pushed to the repository. This ensures that issues are caught early and often. [2]
  • Scheduled Maintenance: Set aside time for regular test maintenance. Just as your codebase evolves, your tests need to evolve with it. Update tests to reflect code changes and evolving requirements.


Unreliable tests can be a headache, but they are not impossible. By understanding the root causes of test unreliability and implementing the strategies outlined in this blog, software engineers can work towards more robust and dependable tests. Remember, fixing unreliable tests is an ongoing process that requires vigilance and effort. With a proactive approach to test reliability, you can boost your confidence in your software’s quality and reduce the headaches that unreliable tests can cause. Happy testing!


  • [1] What is a Flaky Test? (Characteristics, Causes, Resolution) By Shormistha Chatterjee, Community Contributor (BrowserStack)
  • [2] Enabling quality software through CI/CD by PentaTech