In the rapidly evolving landscape of software development, ensuring the stability and reliability of code is paramount. Central to this process are automated tests that verify the integrity of software components whenever changes occur. Yet, a pervasive challenge known as “flaky tests” continues to undermine developers’ efforts. These tests exhibit erratic behavior, sometimes passing and other times failing without any change in the underlying code, leading to wasted time, computational resources, and developer frustration. A groundbreaking study by researchers at Kyushu University, published in the IEEE Transactions on Software Engineering on May 26, 2026, sheds new light on the broader impact of flaky tests, particularly within complex, interconnected software ecosystems like OpenStack.
OpenStack, a flagship open-source cloud computing platform, serves as a critical infrastructure backbone for countless organizations and services worldwide. Its sprawling ecosystem comprises hundreds of interdependent projects, each continuously evolving through contributions from a diverse global developer community. The Kyushu University-led research team, in collaboration with the University of Waterloo, tackled the pressing question of how flaky tests behave not just within isolated projects but across the entire interconnected fabric of software ecosystems. This perspective is vital as many modern software landscapes are no longer isolated silos but intricate webs of shared modules, dependencies, and testing infrastructures.
By meticulously analyzing data from 649 OpenStack projects, the study examined over 29,000 code reviews and more than 73,000 code changes, aiming to quantify and characterize the phenomenon of test flakiness at an unprecedented scale. The results were striking: more than half of the projects (55%) experienced cross-project test instability, where a single flaky test could cause cascading failures in multiple projects. This phenomenon, termed cross-project flakiness, challenges conventional wisdom that flaky tests are confined to individual components and suggests that flakiness acts more like a contagion spreading through the interconnected ecosystem.
Moreover, the study uncovered a second critical phenomenon—termed inconsistent flakiness—where identical tests exhibited varying flaky behavior depending on which project they executed within. This inconsistency not only complicates debugging efforts but also hints at the influence of differing environmental conditions and system configurations across projects. The research identified 1,535 flaky tests responsible for failures across multiple projects and documented 1,105 instances of flaky tests behaving differently depending on the project context. Perhaps most surprisingly, about 70% of unit tests, traditionally considered isolated and stable, also exhibited cross-project instability, thus calling for a reevaluation of assumptions around unit testing reliability.
Delving deeper into the root causes, the researchers pinpointed that many flaky failures were attributable less to defects in the tested code itself and more to environmental and systemic factors. These included vulnerabilities in Continuous Integration (CI) systems such as timing-related issues, unstable server availability, and resource constraints. Additionally, disparities in software dependencies and inconsistencies in test configuration among projects emerged as significant contributors to flaky behavior. Such environmental factors, often shared or replicated across projects within the ecosystem, facilitate the propagation of flakiness, complicating mitigation strategies.
CI systems lie at the heart of modern software development, automatically running suites of tests each time code is committed to ensure ongoing stability. When these pipelines are disrupted by flaky tests, the effect ripples through the development lifecycle—delaying feature integration, inflating testing costs, and eroding developer confidence. The Kyushu team’s findings emphasize that addressing flaky tests requires ecosystem-wide coordination rather than isolated attempts at patching individual projects, underscoring the need for collaboration and harmonization of CI configurations and dependency management across interconnected projects.
Professor Yasutaka Kamei, co-lead of the study, articulates the significance of these findings succinctly: “Our research reveals that test instability transcends project boundaries, emerging as a systemic issue within software ecosystems. Coordinated approaches are critical to curtail the extensive waste of developer time and computational resources caused by flaky tests.” Such coordination could entail shared standards for test environments, unification of dependency versions, and synchronized test execution policies that collectively reduce the incidence of flaky tests.
The study also contributes practical recommendations for tackling this endemic issue. Standardizing CI environments across projects could minimize configuration drift, while advancements in dependency management tools might prevent mismatches that trigger test instability. Furthermore, developing sophisticated detection tools capable of early identification and classification of flaky tests can help developers prioritize investigative efforts, enabling them to distinguish genuine defects from misleading failures efficiently.
Given the growing scale and complexity of software ecosystems today—spanning cloud infrastructure, finance, healthcare, and government systems—the implications of this research extend far beyond OpenStack. As modern societies become increasingly reliant on digital services, the robustness of software testing processes becomes a critical foundation for reliable, secure, and maintainable technology. This study paves the way for innovative, intelligent testing frameworks that can adapt to complex ecosystems and sustain the relentless pace of contemporary software development.
Ultimately, the Kyushu University-led study positions flaky test instability as a collective challenge that demands ecosystem-wide awareness and collaboration. By elevating the discourse from isolated project concerns to systemic ecosystem dynamics, it redefines how software reliability strategies must evolve in the face of growing interdependencies. As Assistant Professor Tao Xiao, the study’s other lead researcher, emphasizes, “This systemic perspective is essential for developing trustworthy testing infrastructures that support the demands of a vibrant digital society.”
The research, titled “Cross-Project Flakiness: A Case Study of the OpenStack Ecosystem,” represents a significant milestone in understanding the intricacies of test instability at scale. It invites software engineers, project maintainers, and industry stakeholders to rethink testing methodologies and embrace coordinated solutions that transcend individual projects. By doing so, the community can mitigate costly inefficiencies and bolster the resilience of critical software infrastructures that underpin modern life.
As software ecosystems continue to expand and interconnect, the urgency to address flaky tests collectively grows. The insights from this study not only illuminate the problem’s breadth but also chart a path forward—one where improved testing stability unlocks faster innovation, enhanced reliability, and smarter resource utilization. This marks a transformative step toward cultivating sustainable software ecosystems equipped to meet the challenges of tomorrow’s digital frontier.
Subject of Research: Software Test Flakiness in Large-Scale Open-Source Ecosystems
Article Title: Cross-Project Flakiness: A Case Study of the OpenStack Ecosystem
News Publication Date: 26-May-2026
Web References:
https://doi.org/10.1109/TSE.2026.3685588
References:
Xiao, T., Wang, D., McIntosh, S., Hata, H., & Kamei, Y. (2026). Cross-Project Flakiness: A Case Study of the OpenStack Ecosystem. IEEE Transactions on Software Engineering. https://doi.org/10.1109/TSE.2026.3685588
Image Credits: Kyushu University
Keywords
Flaky tests, software testing, continuous integration, OpenStack, software ecosystems, test instability, automated testing, software reliability, dependency management, CI environment standardization, cross-project flakiness, software development efficiency
