Continuous learning constitutes a fundamental capability of artificial intelligence systems, enabling them to incrementally assimilate novel information without succumbing to catastrophic forgetting. Recent research has leveraged Pre-Trained Models (PTMs) to enhance continual learning efficacy. Nevertheless, prevailing methodologies typically depend on a singular pre-trained backbone and freeze all pre-trained parameters to mitigate network forgetting, thereby constraining adaptability to emerging tasks. In this study, we introduce an innovative PTM-based framework featuring a Dual-Representation Backbone Architecture (DRBA), which integrates both invariant and evolved representation networks to concurrently capture static and dynamic features. Building upon DRBA, we propose an Adaptive and Expandable Mixture Model (AEMM) that incrementally incorporates new expert modules with minimal parameter overhead to accommodate the learning of each novel task. To further augment adaptability, we develop a Dynamic Adaptive Representation Fusion Mechanism (DARFM) that processes outputs from both representation networks and autonomously generates data-driven adaptive weights, optimizing the contribution of each representation. This mechanism yields an adaptive, semantically enriched composite representation, thereby maximizing positive knowledge transfer. Additionally, we propose a Dynamic Knowledge Calibration Mechanism (DKCM), comprising prediction and representation calibration processes, to ensure consistency in both predictions and feature representations. This approach achieves a balance between stability and plasticity, even when learning complex datasets. Empirical evaluations substantiate that the proposed approach attains state-of-the-art performance.

Plasticity and stability denote the ability to assimilate new tasks while preserving previously acquired knowledge, representing two important concepts in continual learning. Recent research addresses stability by leveraging pre-trained models to provide informative representations, yet the efficacy of these methods is highly reliant on the choice of the pre-trained backbone, which may not yield optimal plasticity. This paper addresses this limitation by introducing a streamlined and potent framework that orchestrates multiple different pre-trained backbones to derive semantically rich multi-source representations. We propose an innovative Multi-Scale Interaction and Dynamic Fusion (MSIDF) technique to process and selectively capture the most relevant parts of multi-source features through a series of learnable attention modules, thereby helping to learn better decision boundaries to boost performance. Furthermore, we introduce a novel Multi-Level Representation Optimization (MLRO) strategy to adaptively refine the representation networks, offering adaptive representations that enhance plasticity. To mitigate over-regularization issues, we propose a novel Adaptive Regularization Optimization (ARO) method to manage and optimize a switch vector that selectively governs the updating process of each representation layer, which promotes the new task learning. The proposed MLRO and ARO approaches are collectively optimized within a unified optimization framework to achieve an optimal trade-off between plasticity and stability. Our extensive experimental evaluations reveal that the proposed framework attains state-of-the-art performance. The source code of our algorithm is available at https://github.com/CL-Coder236/LMSRR.

Continual learning requires the model to continually capture novel information without forgetting prior knowledge. Nonetheless, existing studies predominantly address the catastrophic forgetting, often neglecting enhancements in model robustness. Consequently, these methodologies fall short in real-time applications, such as autonomous driving, where data samples frequently exhibit noise due to environmental and lighting variations, thereby impairing model efficacy and causing safety issues. In this paper, we address robustness in continual learning systems by introducing an innovative approach, the Dynamic Siamese Expansion Framework (DSEF) that employs a Siamese backbone architecture, comprising static and dynamic components, to facilitate the learning of both global and local representations over time. Specifically, the proposed framework dynamically generates a lightweight expert for each novel task, leveraging the Siamese backbone to enable rapid adaptation. A novel Robust Dynamic Representation Optimization (RDRO) approach is proposed to incrementally update the dynamic backbone by maintaining all previously acquired representations and prediction patterns of historical experts, thereby fostering new task learning without inducing detrimental knowledge transfer. Additionally, we propose a novel Robust Feature Fusion (RFF) approach to incrementally amalgamate robust representations from all historical experts into the expert construction process. A novel mutual information-based technique is employed to derive adaptive weights for feature fusion by assessing the knowledge relevance between historical experts and the new task, thus maximizing positive knowledge transfer effects. A comprehensive experimental evaluation, benchmarking our approach against established baselines, demonstrates that our method achieves state-of-the-art performance even under adversarial attacks.

Extant studies predominantly address catastrophic forgetting within a simplified continual learning paradigm, typically confined to a singular data domain. Conversely, real-world applications frequently encompass multiple, evolving data domains, wherein models often struggle to retain many critical past information, thereby leading to performance degradation. This paper addresses this complex scenario by introducing a novel dynamic expansion approach called Learning Expandable and Adaptable Representations (LEAR). This framework orchestrates a collaborative backbone structure, comprising global and local backbones, designed to capture both general and task-specific representations. Leveraging this collaborative backbone, the proposed framework dynamically create a lightweight expert to delineate decision boundaries for each novel task, thereby facilitating the prediction process. To enhance new task learning, we introduce a novel Mutual Information-Based Prediction Alignment approach, which incrementally optimizes the global backbone via a mutual information metric, ensuring consistency in the prediction patterns of historical experts throughout the optimization phase. To mitigate network forgetting, we propose a Kullback–Leibler (KL) Divergence-Based Feature Alignment approach, which employs a probabilistic distance measure to prevent significant shifts in critical local representations. Furthermore, we introduce a novel Hilbert-Schmidt Independence Criterion (HSIC)-Based Collaborative Optimization approach, which encourages the local and global backbones to capture distinct semantic information in a collaborative manner, thereby mitigating information redundancy and enhancing model performance. Moreover, to accelerate new task learning, we propose a novel Expert Selection Mechanism that automatically identifies the most relevant expert based on data characteristics. This selected expert is then utilized to initialize a new expert, thereby fostering positive knowledge transfer. This approach also enables expert selection during the testing phase without requring any task information. Empirical results demonstrate that the proposed framework achieves state-of-the-art performance.

Finding non-crashing functional bugs for Android apps is challenging for both manual testing and automated GUI testing techniques. This paper introduces and designs a general and practical testing technique based on the idea of property-based testing for finding such bugs. Specifically, our technique incorporates (1) a property description language (PDL) to allow specifying desired app properties, and (2) two exploration strategies as the input generators for effectively validating the properties. We implemented our technique as a tool named Kea and evaluated it on 124 historical bugs from eight real-world, popular Android apps. Our evaluation shows that our PDL can specify all the app properties violated by these historical bugs, demonstrating its generability for finding functional bugs. Kea successfully found 66 (68.0%) and 92 (94.8%) of the 97 historical bugs in scope under the two exploration strategies, demonstrating its practicability. Moreover, Kea found 25 new functional bugs on the latest versions of these eight apps, given the specified properties. To date, all these bugs have been confirmed, and 21 have been fixed. In comparison, prior state-of-the-art techniques found only 13 (13.4%) historical bugs and 1 new bug. We have made all the artifacts publicly available at https://github.com/ecnusse/Kea.

Inter-component communication (ICC) is a key mechanism in Android. It utilizes intents to achieve the communications between different components in the apps. Thus, the successful execution of ICCs (named ICC calls) is fundamental to the app operations. However, existing testing tools for Android seldom explicitly consider these ICC calls, which may fail to find those ICC-related bugs. To this end, we propose a novel ICC-guided exploration strategy to effectively find the ICC-related bugs. Our idea is that, we can (1) build an ICC call graph from the app under test, and (2) use this graph to guide the exploration toward exercising the ICC calls. To achieve this idea, we design this ICC-guided exploration strategy based on Q-learning, a classic reinforcement learning algorithm. Specifically, the reward function explicitly considers the number of explored intents, the number of promising-to-explore intents and the exploration order of explored intents to improve testing effectiveness. Moreover, to build a more complete ICC call graph, we design a graph enhancement exploration strategy also based on Q-learning to complement the call graph construction via static analysis. We have implemented our idea as an automated testing tool IccDroid. The evaluation on 28 real-word Android apps shows that IccDroid can effectively find the most number of ICC-related bugs within the same testing time, compared to existing testing tools — the bugs found by IccDroid are 1.7~2.7 times more than the others. So far, IccDroid has found 13 previously unknown ICC-related bugs, all of which have been confirmed by the app developers and five have already been fixed.

Android apps are ubiquitous and serve many aspects of our daily lives. Ensuring their functional correctness is crucial for their success. To date, we still lack a general and in-depth understanding of functional bugs, which hinders the development of practices and techniques to tackle functional bugs. To fill this gap, we conduct the first systematic study on 399 functional bugs from 8 popular open-source and representative Android apps to investigate the root causes, bug symptoms, test oracles, and the capabilities and limitations of existing testing techniques. This study took us substantial effort. It reveals several new interesting findings and implications which help shed light on future research on tackling functional bugs. Furthermore, findings from our study guided the design of a proof-of-concept differential testing tool, RegDroid, to automatically find functional bugs in Android apps. We applied RegDroid on 5 real-world popular apps, and successfully discovered 14 functional bugs, 10 of which were previously unknown and affected the latest released versions—all these 10 bugs have been confirmed and fixed by the app developers. Specifically, 10 out of these 14 found bugs cannot be found by existing testing techniques. We have made all the artifacts (including the dataset of 399 functional bugs and RegDroid) in our work publicly available at https://github.com/Android-Functional-bugs-study/home.

Like many software applications, data manipulation functionalities( DMFs ) are prevalent in Android apps, which perform the common CRUD operations (create, read, update, delete) to handle app-specific data. Thus, ensuring the correctness of these DMFs is fundamentally important for many core app functionalities. However, the bugs related to DMFs (named as data manipulation errors, DMEs ), especially those non-crashing logic ones, are prevalent but difficult to find. To this end, inspired by property-based testing, we introduce a property-based fuzzing approach to effectively finding DMEs in Android apps. Our key idea is that, given some type of app data of interest, we randomly interleave its relevant DMFs and other possible events to explore diverse app states for thorough validation. Specifically, our approach characterizes DMFs in (data) model-based properties and leverage the consistency between the data model and the UI layouts as the handler to do property checking. The properties of DMFs are specified by human according to specific app features. To support the application of our approach, we implemented an automated GUI testing tool, PBFDroid. We evaluated PBFDroid on 20 real-world Android apps, and successfully found 30 unique and previously unknown bugs in 18 apps. Out of the 30 bugs, 29 of which are DMEs (22 are non-crashing logic bugs, and 7 are crash ones). To date, 19 have been confirmed and 9 have already been fixed. Many of these bugs are non-trivial and lead to different types of app failures. Our further evaluation confirms that none of the 22 non-crashing DMEs can be found by the state-of-the-art techniques. In addition, a user study shows that the manual cost of specifying the DMF properties with the assistance of our tool is acceptable. Overall, given accurate DMF properties, our approach can automatically find DMEs without any false positives. We have made all the artifacts publicly available at:https:// github.com/ property-based-fuzzing/ home.

Android, the most popular mobile system, offers a number of user-configurable system settings (e.g., network, location, and permission) for controlling devices and apps. Even popular, well-tested apps may fail to properly adapt their behaviors to diverse setting changes, thus frustrating their users. However, there exists no effort to systematically investigate such defects. To this end, we conduct thefirstlarge-scale empirical study to understand and characterize thesesystem setting-related defects(in short as “setting defects”), whichreside in apps and are triggered by system setting changes. We devote substantial manual effort (over four person-months) to analyze 1,074 setting defects from 180 popular apps on GitHub. We investigate the impact, root causes, and consequences of these setting defects and their correlations. We find that (1) setting defects have a wide impact on apps’ correctness with diverse root causes, (2) the majority of these defects ($\approx$70.7%) cause non-crashing (logic) failures, and (3) some correlations exist between the setting categories, root causes, and consequences. Motivated and informed by these findings, we propose two bug-finding techniques that can synergistically detect setting defects from both the GUI and code levels. Specifically, at the GUI level, we design and introducesetting-wise metamorphic fuzzing, thefirstautomated dynamic testing technique to detect setting defects (causing crashandnon-crashing failures, respectively) for Android apps. We implement this technique as an end-to-end, automated GUI testing tool namedSetDroid. At the code level, we distill two major fault patterns and implement a static analysis tool namedSetCheckerto identify potential setting defects. We evaluateSetDroidandSetCheckeron 26 popular, open-source Android apps, and they find 48 unique, previously-unknown setting defects. To date, 35 have been confirmed and 21 have been fixed by app developers. We also applySetDroidandSetCheckeron five highly popular industrial apps, namely WeChat, QQMail, TikTok, CapCut, and AlipayHK, all of which each have billions of monthly active users.SetDroidsuccessfully detects 17 previously unknown setting defects in these apps’ latest releases, and all defects have been confirmed and fixed by the app vendors. After that, we collaborate with ByteDance and deploy these two bug-finding techniques internally to stress-test TikTok, one of its major app products. Within a two-month testing campaign,SetDroidsuccessfully finds 53 setting defects, andSetCheckerfinds 22 ones. So far, 59 have been confirmed and 31 have been fixed. All these defects escaped from prior developer testing. By now,SetDroidhas been integrated into ByteDance's official app testing infrastructure namedFastBotfor daily testing. These results demonstrate the strong effectiveness and practicality of our proposed techniques.

Android, the most popular mobile system, offers a number of user-configurable system settings (e.g., network, location, and permission) for controlling devices and apps. Even popular, well-tested apps may fail to properly adapt their behaviors to diverse setting changes, thus frustrating their users. However, there exists no effort to systematically investigate such defects. To this end, we conduct the first empirical study to understand the characteristics of these setting-related defects (in short as "setting defects"), which reside in apps and are triggered by system setting changes. We devote substantial manual effort (over three person-months) to analyze 1,074 setting defects from 180 popular apps on GitHub. We investigate their impact, root causes, and consequences. We find that setting defects have a wide, diverse impact on apps' correctness, and the majority of these defects (≈70.7%) cause non-crash (logic) failures, and thus could not be automatically detected by existing app testing techniques due to the lack of strong test oracles. Motivated and guided by our study, we propose setting-wise metamorphic fuzzing, the first automated testing approach to effectively detect setting defects without explicit oracles. Our key insight is that an app's behavior should, in most cases, remain consistent if a given setting is changed and later properly restored, or exhibit expected differences if not restored. We realize our approach in SetDroid, an automated, end-to-end GUI testing tool, for detecting both crash and non-crash setting defects. SetDroid has been evaluated on 26 popular, open-source apps and detected 42 unique, previously unknown setting defects in 24 apps. To date, 33 have been confirmed and 21 fixed. We also apply SetDroid on five highly popular industrial apps, namely WeChat, QQMail, TikTok, CapCut, and AlipayHK, all of which each have billions of monthly active users. SetDroid successfully detects 17 previously unknown setting defects in these apps' latest releases, and all defects have been confirmed and fixed by the app vendors. The majority of SetDroid-detected defects (49 out of 59) cause non-crash failures, which could not be detected by existing testing tools (as our evaluation confirms). These results demonstrate SetDroid's strong effectiveness and practicality.

Android apps are GUI-based event-driven software and have become ubiquitous in recent years. Obviously, functional correctness is critical for an app’s success. However, in addition to crash bugs, non-crashing functional bugs (in short as “non-crashing bugs” in this work) like inadvertent function failures, silent user data lost and incorrect display information are prevalent, even in popular, well-tested apps. These non-crashing functional bugs are usually caused by program logic errors and manifest themselves on the graphic user interfaces (GUIs). In practice, such bugs pose significant challenges in effectively detecting them because (1) current practices heavily rely on expensive, small-scale manual validation ( the lack of automation ); and (2) modern fully automated testing has been limited to crash bugs ( the lack of test oracles ). This paper fills this gap by introducing independent view fuzzing , a novel, fully automated approach for detecting non-crashing functional bugs in Android apps. Inspired by metamorphic testing, our key insight is to leverage the commonly-held independent view property of Android apps to manufacture property-preserving mutant tests from a set of seed tests that validate certain app properties. The mutated tests help exercise the tested apps under additional, adverse conditions. Any property violations indicate likely functional bugs for further manual confirmation. We have realized our approach as an automated, end-to-end functional fuzzing tool, Genie. Given an app, (1) Genie automatically detects non-crashing bugs without requiring human-provided tests and oracles (thus fully automated ); and (2) the detected non-crashing bugs are diverse (thus general and not limited to specific functional properties ), which set Genie apart from prior work. We have evaluated Genie on 12 real-world Android apps and successfully uncovered 34 previously unknown non-crashing bugs in their latest releases — all have been confirmed, and 22 have already been fixed. Most of the detected bugs are nontrivial and have escaped developer (and user) testing for at least one year and affected many app releases, thus clearly demonstrating Genie’s effectiveness. According to our analysis, Genie achieves a reasonable true positive rate of 40.9%, while these 34 non-crashing bugs could not be detected by prior fully automated GUI testing tools (as our evaluation confirms). Thus, our work complements and enhances existing manual testing and fully automated testing for crash bugs.