Improve Test Coverage Research Articles

Assessing the effect of COVida orphans and vulnerable children support services on viral load coverage and suppression among children and adolescents living with HIV in four provinces in Mozambique

ABSTRACT Orphans and vulnerable children (OVC) programs focusing on improving HIV outcomes for children and adolescents living with HIV (C&ALHIV) may improve viral load (VL) testing coverage, a critical step toward achieving VL suppression. In Mozambique, we conducted a retrospective medical record review comparing VL testing coverage and suppression between C&ALHIV receiving OVC support and two cohorts of non-participants constructed using propensity score matching. We collected data for 25,783 C&ALHIV in Inhambane, Maputo City, Nampula, and Tete between October 2020-September 2021. Unadjusted rates of VL testing were 62.9% among OVC participants compared with 39.2% and 50.4% of non-participants in OVC support and non-OVC support districts, respectively. In multivariate models, OVC participants were 18 and 10 percentage points more likely to have received a VL test than non-participants in OVC districts (p < 0.01) and non-OVC districts (p < 0.01), respectively. OVC participants under 5 years old were significantly more likely to have received a VL test than their same-age counterparts in both comparison groups. Overall, the OVC program did not demonstrate significant effects on VL suppression. This approach could be replicated in other contexts to improve testing coverage. It is crucial that clinical partners and governments continue to share data to enable timely monitoring through OVC programming.

Magnitude of HIV Index Case Testing among HIV Positive Clients Attending ART Clinic in University of Gondar Comprehensive Specialized Hospital, Northwest Ethiopia, 2023

Background: Index case testing is the provision of HIV testing services to family members or sexual partners of individuals already diagnosed with HIV. Its promotion stems from its potential to detect new cases, improve testing coverage, enhance ART retention, and provide convenience to affected families. Although evidence on index case testing in Ethiopia, particularly in the study area, is lacking, even, it is regarded as a crucial strategy for reducing HIV transmission among those unaware of their HIV status. Objective: This study aimed to determine the prevalence and associated factors with HIV index testing in Northwest Ethiopia. Methods: The study utilized an institution-based cross-sectional study design. The recruitment of 387 HIV-positive clients was done using a simple random sampling technique, and structured interviewer-administered questionnaires were employed for data collection. The collected data was entered into Kobo Collect software and later exported to STATA version 16 for analysis. In binary logistic regression, variables with a p-value below 0.25 were considered as candidates for multivariate logistic regression. An association was assessing if the p-value was below 0.05 with a 95% confidence interval. Results: In the study, 380 (98.19% of participants) underwent the interview. The prevalence of HIV index case testing service was 38.7% (CI: 36.45% to 42.03%). Significant associations were observed between HIV index case testing and certain factors. Those with a higher education level (college and above) had 1.21 times higher odds (AOR) of undergoing index case testing (CI: 1.05 to 3.11). Married individuals had 2.30 times higher odds of receiving index case testing (AOR) (CI: 1.98 to 4.20). Participants engaged in work for monetary compensation had 1.66 times higher odds of undergoing index case testing (AOR) (CI: 1.58 to 4.71). Conclusion: The utilization of index case testing service was lower in this study compared to previous research. Higher education level (college and above), occupation involving work for monetary compensation, and being married were associated with HIV index case testing. To enhance uptake, community-based education programs and targeted training for HIV-positive individuals are recommended. These measures can raise awareness and encourage greater participation in index case testing.

Missed opportunities for integrated testing: An Evaluation of the implementation of TB and HIV EID Testing on the GeneXpert platform in Lesotho

Introduction: Integrated testing of TB and HIV can improve health outcomes and save costs. The GeneXpert (GX) instrument, a multi-disease testing platform, can allow for simultaneous HIV and TB testing. However, utilization of the platform for integrated testing remains suboptimal, and there are operational barriers to implementing integrated TB and HIV testing.&#x0D; Methods: We evaluated the implementation of TB and HIV testing on the GX instrument for early infant detection (EID) of HIV and tuberculosis (TB) testing in thirteen health facilities in Lesotho. The data collection process used a survey questionnaire, semi-structured interviews, and a review of records at each health facility. Data was collected for the period 2017 and 2019.&#x0D; Results: All thirteen health facilities had at least one GX instrument for TB or EID testing. In 2017, the average utilization rate for the GX instrument for TB and EID testing was 63% and 24%, while in 2019, the average utilization rate was 61% for TB testing and 27% for EID. However, none of the health facilities included testing for TB and HIV on the same GX instrument simultaneously. In general, utilization rates were sufficiently low that all the HIV and TB tests undertaken in 2017 and 2019 could have been performed using only the instruments currently dedicated to TB testing. All except for three sites (Scott, Motebang and Maluti) where the testing rates were high. &#x0D; Conclusion and Policy Implications: Much progress has been made in integrating TB and HIV activities in Africa. However, there is a missed opportunity for the integration of testing for TB and HIV on the GX instrument, which could save costs.&#x0D; This evaluation highlights areas that need more focus and more detailed diagnostic network optimization exercises to improve service delivery and allocate stocks, staff, equipment, and training. Better coordination of donor support or increased flexibility in reporting of use will be important to maximize the use of resources, where integration may be more effective than purchasing new equipment. Monitoring and evaluation should be a routine part of the implementation and should be budgeted and demanded by policymakers and donors. Health facilities may require additional resources and technical support to improve data collection, analysis, and dissemination.&#x0D; In conclusion, areas highlighted in this evaluation merit further exploration, such as the need to understand integrated testing models, including what works, why, and for which target groups. This will allow for effective targeted interventions to improve testing coverage across several diseases especially taking advantage of the multi-disease testing platforms.&#x0D; &#x0D;

Good performance of syphilis rapid diagnostic test kits among young key populations in Thailand.

The prevalence of syphilis is increasing among adolescents and young adults (AYAs) globally. Use of syphilis rapid diagnostic treponemal tests (RDTs) may improve test coverage and same-day treatment. This study aims to determine sensitivity and specificity of two syphilis RDTs. A cross-sectional study was conducted in men who have sex with men and transgender women aged 15-24years attending a sexual health clinic in Bangkok. Syphilis RDTs used were Determine Syphilis TP and Bioline Syphilis 3.0, using whole blood from finger pricks and venipuncture. Treponemal pallidum electrochemiluminescence assay was used as standard reference. From February to July 2022, 200 AYAs with a mean age 21.1 (SD2.1) years were enrolled, including 50 (25.0%) living with HIV. Prevalence of syphilis was 10.5% (95%CI 6.6-15.6), which was higher among AYAs living with HIV (22.0%) compared with AYAs unaffected by HIV (6.7%). Sensitivities of Determine Syphilis TP and Bioline Syphilis 3.0 were 85.7% (95%CI 63.7-97.0) and 66.7% (95%CI 43.0-85.4), respectively. Specificity of both RDTs was 100% (95%CI 98.0-100.0). Performance of RDTs was similar for both specimens. Syphilis RDTs have high sensitivity and specificity in diagnosing syphilis. It should be considered for use in sexual health clinics with high syphilis prevalence to initiate treatment promptly.

SPAR: A New Test-Point Insertion Using Shared Points for Area Overhead Reduction

Test-point insertion (TPI) is an effective technique for improving the random pattern testability of digital circuits. However, it introduces area and performance overhead. Because the test-point area takes a significant portion of the test logic area, many techniques have been studied to reduce the area impact, such as sharing a control point (CP) driver with multiple CPs or replacing a dedicated CP driver with an existing flip-flop. This article proposes shared point insertion for area overhead reduction (SPAR) to simultaneously reduce the area impact of CPs and observation points (OPs). SPAR inserts a shared point instead of inserting a pair of CP and OP individually. Consequently, the pair of CP and OP is provided requirements, such as a control signal or propagation path from each other through the shared point—accordingly, the shared point simultaneously functions as the CP and OP. Furthermore, a signal that drives a shared point can be chosen to ensure the fair propagation of faults. The proposed flow searches for appropriate CP–OP pairs to insert shared points while avoiding potential issues from the newly created path. Experimental results on benchmarks demonstrate that SPAR can significantly reduce area overhead caused by test points while achieving almost identical or even slightly improved test coverage.

Diagnostic accuracy of pooling urine, anorectal, and oropharyngeal specimens for the detection of Chlamydia trachomatis and Neisseria gonorrhoeae: a systematic review and meta-analysis

BackgroundScreening for Chlamydia trachomatis (CT) and Neisseria gonorrhoeae (NG) at genital and extragenital sites is needed for most key populations, but molecular diagnostic tests for CT/NG are costly. We aimed to determine the accuracy of pooled samples from multiple anatomic sites from one individual to detect CT/NG using the testing of a single sample from one anatomic site as the reference.MethodsIn this systematic review and meta-analysis, we searched five databases for articles published from January 1, 2000, to February 4, 2021. Studies were included if they contained original data describing the diagnostic accuracy of pooled testing compared with single samples, resource use, benefits and harms of pooling, acceptability, and impact on health equity. We present the pooled sensitivities and specificities for CT and NG using a bivariate mixed-effects logistic regression model. The study protocol is registered in PROSPERO, an international database of prospectively registered systematic reviews (CRD42021240793). We used GRADE to evaluate the quality of evidence.ResultsOur search yielded 7814 studies, with 17 eligible studies included in our review. Most studies were conducted in high-income countries (82.6%, 14/17) and focused on men who have sex with men (70.6%, 12/17). Fourteen studies provided 15 estimates for the meta-analysis for CT with data from 5891 individuals. The pooled sensitivity for multisite pooling for CT was 93.1% [95% confidence intervals (CI) 90.5–95.0], I2=43.3, and pooled specificity was 99.4% [99.0–99.6], I2=52.9. Thirteen studies provided 14 estimates for the meta-analysis for NG with data from 6565 individuals. The pooled sensitivity for multisite pooling for NG was 94.1% [95% CI 90.9–96.3], I2=68.4, and pooled specificity was 99.6% [99.1–99.8], I2=83.6. Studies report significant cost savings (by two thirds to a third).ConclusionMultisite pooled testing is a promising approach to improve testing coverage for CT/NG in resource-constrained settings with a small compromise in sensitivity but with a potential for significant cost savings.

Model-based testing in practice: An experience report from the web applications domain

In the context of a software testing company, we have deployed the model-based testing (MBT) approach to take the company’s test automation practices to higher levels of maturity and capability. We have chosen, from a set of open-source/commercial MBT tools, an open-source tool named GraphWalker, and have pragmatically used MBT for end-to-end test automation of several large web and mobile applications under test. The MBT approach has provided, so far in our project, various tangible and intangible benefits in terms of improved test coverage (number of paths tested), improved test-design practices, and also improved real-fault detection effectiveness. The goal of this experience report (applied research report), done based on “action research”, is to share our experience of applying and evaluating MBT as a software technology (technique and tool) in a real industrial setting. We aim at contributing to the body of empirical evidence in industrial application of MBT by sharing our industry-academia project on applying MBT in practice, the insights that we have gained, and the challenges and questions that we have faced and tackled so far. We discuss an overview of the industrial setting, provide motivation, explain the events leading to the outcomes, discuss the challenges faced, summarize the outcomes, and conclude with lessons learned, take-away messages, and practical advices based on the described experience. By learning from the best practices in this paper, other test engineers could conduct more mature MBT in their test projects.

Prediction Model and Experimental Study on Braking Distance under Emergency Braking with Heavy Load of Escalator

In order to study the relationship between the braking distance and the load of escalator and realize the prediction of the rated load braking distance with a little load, the method of combining theoretical analysis and experimental research is used. First, the dynamic characteristics of the escalator during emergency braking are analyzed, and the prediction model of the braking distance of the escalator under different loads is derived based on the law of conservation of energy. Furthermore, the influence coefficients under different loads were determined through experimental studies, the model was revised, and the concept of equivalent no-load kinetic energy (ENKE) was proposed. The research shows that the braking distance of the escalator increases nonlinearly with the increase in load. When the no-load braking distance and the 25% rated load braking distance change greatly, the braking distance increases faster as the load increases; the escalators with large brake force have a small ENKE and are easy to stop. Otherwise, it is difficult to stop. The test results show that the comparison between the predicted value of the prediction model and the measured value has a maximum error of 2.7%, and the maximum error at rated load is only 2.0%, which fully meets the needs of engineering measurement. And the prediction method reduces test costs, enhances test security, and improves test coverage.

Preferred HIV Testing Modalities Among Adolescent Girls and Young Women in Kenya

PurposeTo improve testing coverage, it is imperative to determine adolescent girls and young women (AGYW) preferences about HIV testing modality and where they prefer receiving services. MethodsParticipants were enrolled between May 2017 and April 2018 from three sites in Homa Bay County, Nyanza region, western Kenya. We explored two recruitment approaches (home-based vs. mobile-event based) and three HIV testing options (oral self-test, staff-administered, or referral to health facility). Exact logistic regression compared yield of newly diagnosed HIV and high-risk HIV-negatives from the recruitment and testing option strategies. ResultsA total of 1,198 participants were enrolled, 1,046 (87.3%) at home and 152 (12.7%) at mobile events. Most participants (928, 77.5%) chose staff-aided testing either at home or at a mobile event; 268 (22.4%) chose self-testing; and only 2 (.2%) chose facility referral. Prevalence of newly diagnosed HIV-positives was 2.7% (32/1,198) and 36.8% (429/1,166) of HIV-negative AGYW were identified as high risk. We identified more newly diagnosed HIV infection among AGYW recruited at mobile events than at home (OR = 3.11; 95% CI: 1.33–6.74; p = .02). High-risk status was related to neither recruitment strategy nor testing modality. Older age was associated with increased odds of selecting an oral self-test (OR = 1.85; 95% CI: 1.06–3.22). ConclusionsMore than one-third of AGYW were at elevated risk of HIV infection, and those unaware of their HIV infection were more likely to be identified at a mobile outreach. Though self-testing was not the dominant preferred strategy, self-tests were performed accurately and with high confidence. These findings can help inform efficient identification of undiagnosed HIV infection and high risk for seroconversion among AGYW in similar settings.

Reinforcement Learning for Optimizing Test Case Execution in Automated Testing

This study explores the use of reinforcement learning (RL) techniques to optimize test case execution in automated testing frameworks, addressing the inefficiencies of traditional testing methods. The primary research problem involves enhancing testing efficiency, improving coverage, and reducing redundancy through intelligent RL-based optimization. The study employed a design that integrated RL algorithms into automated testing frameworks, involving the development and training of an RL model, followed by empirical evaluation. ajor findings indicate that RL-based optimization significantly reduced test case execution time, improved test coverage, and minimized redundancy compared to conventional methods. The RL model dynamically adjusted test case sequences based on real-time feedback, leading to enhanced efficiency and more comprehensive testing. The study concludes that RL techniques offer a promising approach to overcoming traditional testing limitations, demonstrating tangible benefits in real-world scenarios. To put in a nutshell, RL-based optimization effectively addresses key challenges in automated testing, offering a more adaptive and efficient strategy for test case execution.

About the features of the verification of VLSI class “System on a chip” for complex information systems

The article discusses the hierarchical levels of the verification process for VLSI of the System-on-Chipclass, as well as information systems built on their basis. The increasing complexity of modern information systems creates additional requirements for the composition and complexity of the verification of such systems, including the early stages of their development. An approach to verification is proposed using a combination of software tools for modeling digital circuits at the lower levels of abstraction and specialized verification tools developed for a specific information system and implementing verification primarily at the system level. The proposed approach will enhance the performance of VLSI modeling of the System-on-Chip class, which will improve the reliability of verification of complex systems by improving test coverage. It is noted that when connecting mutually asynchronous fragments of VLSI it is necessary to carry out modeling at a high level, able to identify problems of data transmission between individual synchronous subsystems.

A Method for Improving Test Coverage by Improving Test Cases

With the development of aerospace industry, the complexity of aerospace software is increasing, and the statue of software testing is becoming more and more important. The coverage test is an important method of testing the code logic defects. In order to meet the particularity of embedded aerospace software, this paper proposes a method to improve test coverage by improving test cases, which reducing the number of test cases and improving the efficiency of testing, thereby improving the effectiveness of test coverage. Based on five kinds of optimization types, the full text reduces the number of test cases and removes redundancy in order to improve the efficiency of test cases. While improving the test coverage, the method improves overall test efficiency, finally achieves the expected effect and reduces the cost of software development.

Performance of point-of-care birth HIV testing in primary health care clinics: An observational cohort study.

BackgroundFailure to timely diagnose HIV in infants is a major barrier for scaling-up paediatric antiretroviral treatment (ART). WHO recommends birth testing for earlier diagnosis and to improve test coverage, but current diagnosis takes 2–3 weeks to complete, thereby limiting the ability of care givers to provide follow-on care, especially in low-resource settings. We evaluated the benefit of implementing rapid diagnosis of HIV at birth in primary health care maternity wards in Mozambique.Methods and findingsInfants born to HIV-infected mothers delivering consecutively at eight primary health care clinics were tested within 24 hours of delivery using on-site POC (Alere q HIV1/2 Detect) and standard laboratory (Roche COBAS AmpliPrep/TaqMan HIV-1 qualitative assay v2.0) testing. Infants were also tested at 4–6 weeks of age with both assays. Of 2,350 HIV-exposed infants enrolled in this implementation research study, 33 tested HIV-positive at birth on both assays. Sensitivity and specificity of POC testing compared with laboratory testing at birth were 100% (95% CI 89·4–100·0) and 100% (95% CI 99·8–100·0), respectively. At 4–6 weeks of age, 61 infants were identified as HIV-positive; of these 29 (47·5%) had a positive test at birth. Testing at both birth and 4–6 weeks identified 71 HIV-positive infants compared with 61 infants by testing at 4–6 weeks alone, a 16% increase. Two infants tested positive at birth but tested HIV-negative during follow-up.ConclusionsAdding POC birth testing to the 4–6 week screen may increase access to HIV diagnosis and expedite ART initiation in primary health care settings within low resource settings. Guidance on appropriate confirmatory HIV testing algorithms for birth testing is needed.

Sequential Test Decompressors with Fast Tester Bits Wide-Spreading

Usually, test pattern decompressors with dynamic reseeding are reset before starting a new test pattern decoding. The first few scan chain slices are then filled with test vectors that have lower decoding ability as the number of free variables is limited by the test access mechanism bandwidth. We have found that even within this limitation, it is possible to improve the decodability by creating fast and wide-spreading as many as possible independent linear combinations of the tester bits and using them for the scan chain loading. We evaluated features influencing the decompression quality and the hardware overhead for different decompressor principles. According to the evaluation results, we proposed a decompressor combining a XOR network and a linear feedback shift register (LFSR)-like automaton; we place the XOR network on the LFSR inputs. We demonstrate that due to this arrangement, the combined decompressor can be used without any phase shifter or state skipping ability of the LFSR. We have experimentally verified that adopting the proposed decompressor structure improves test coverage, saves the hardware resources and shortens the test application time.

Evaluating point-of-care testing for glycosylated haemoglobin in public sector primary care facilities in the Western Cape, South Africa.

Diabetes mellitus contributes significantly to the burden of disease in South Africa (SA). Monitoring of glycaemic control with glycosylated haemoglobin (HbA1c) is recommended, even though current laboratory-based testing does not support immediate clinical decision-making. To evaluate the costs and consequences for quality of care by introducing point-of-care (POC) testing for HbA1c for patients with type 2 diabetes at community health centres in Cape Town, SA. A quasi-experimental study was conducted at two control and two intervention sites in the same sub-district. The DCA Vantage Analyzer (Siemens, Germany) for POC testing was introduced at the intervention sites for 12 months. Patients were randomly selected from the diabetes register at the intervention (n=300) and control (n=300) sites, respectively, and data were collected from patient records at baseline and 12 months. Focus group interviews were performed at the intervention sites. Technical quality and cost implications were evaluated. POC testing was feasible, easy to integrate into the organisation of care, resulted in more immediate feedback to patients (p&lt;0.001) and patients appeared more satisfied. POC testing did not improve test coverage, treatment intensification, counselling or glycaemic control. There was an incremental cost of ZAR2 110 per 100 tests. Compliance with quality control was poor, although control tests showed good reliability. This study does not support the introduction of POC testing for HbA1c in public sector primary care practice in the current context. POC testing should be evaluated further in combination with interventions to overcome clinical inertia and strengthen primary healthcare.

Evaluating point-of-care testing for glycosylated haemoglobin in public sector primary care facilities in the Western Cape, South Africa

Background. Diabetes mellitus contributes significantly to the burden of disease in South Africa (SA). Monitoring of glycaemic control with glycosylated haemoglobin (HbA1c) is recommended, even though current laboratory-based testing does not support immediate clinical decision-making. Objectives. To evaluate the costs and consequences for quality of care by introducing point-of-care (POC) testing for HbA1c for patients with type 2 diabetes at community health centres in Cape Town, SA. Methods. A quasi-experimental study was conducted at two control and two intervention sites in the same sub-district. The DCA Vantage Analyzer (Siemens, Germany) for POC testing was introduced at the intervention sites for 12 months. Patients were randomly selected from the diabetes register at the intervention (n=300) and control (n=300) sites, respectively, and data were collected from patient records at baseline and 12 months. Focus group interviews were performed at the intervention sites. Technical quality and cost implications were evaluated. Results. POC testing was feasible, easy to integrate into the organisation of care, resulted in more immediate feedback to patients (p&lt;0.001) and patients appeared more satisfied. POC testing did not improve test coverage, treatment intensification, counselling or glycaemic control. There was an incremental cost of ZAR2 110 per 100 tests. Compliance with quality control was poor, although control tests showed good reliability. Conclusion. This study does not support the introduction of POC testing for HbA1c in public sector primary care practice in the current context. POC testing should be evaluated further in combination with interventions to overcome clinical inertia and strengthen primary healthcare.

RGA: A lightweight and effective regeneration genetic algorithm for coverage-oriented software test data generation

ContextGenetic algorithm (GA) is an important intelligent method in the area of automatic software test data generation. However, existing GAs tend to get trapped in the local optimal solution, leading to population aging, which can significantly reduce the benefits of GA-based software testing and increase cost and effort. Although much attention has been focused on solving this problem by improving chromosome population, genetic operations, and genetic parameters adjustment, the applicability of most of the algorithms proposed is often narrow because of the complex operations involved and nondeterminism inherited from traditional GAs. ObjectivesThis paper proposes a new algorithm called the regenerate genetic algorithm (RGA), which is based on a new simple, stable, and easy-to-implement regeneration strategy that involves judging the population aging process. MethodsWe propose a new regeneration strategy—called Regenerate Genetic Algorithm (RGA)—that solves these problems easily and effectively. The proposed strategy defines population aging factors and process in order to determine the degree of population aging. Subsequently, when population aging has reached a certain limit, a population regeneration operation is triggered. In contrast to other improved methods, the proposed regeneration strategy for population aging easily achieves a stronger ability to jump out of the local optimal solution, thereby preventing population aging and effectively improving test coverage, without modifying any parameter of the original GA. ResultsThe proposed algorithm is experimentally evaluated by comparing it to the basic GA, Random Testing (RT) and several other methods in terms of both efficiency and effectiveness on the Siemens Suite of test programs and a more complex real program. The results obtained indicate that the proposed algorithm can effectively increase search efficiency, restrain population aging, increase test coverage, and reduce the number of test cases. ConclusionRGA has better optimization ability than the conventional algorithms, especially for large-scale and highly complex programs.

Introducing Combinatorial Testing in a Large Organization

A two-year study of eight pilot projects to introduce combinatorial testing in a large aerospace corporation found that the new methods were practical, significantly lowered development costs, and improved test coverage by 20 to 50 percent.

Harzard-Based ATPG for Improving Delay Test Quality

Fault coverage is a popular test criterion in delay testing. In order to improve test coverage, an efficient automatic test pattern generation (ATPG) method especially aimed at hazard-based detection condition (HDC), referred to as HDC test generation, is proposed. The proposed method effectively enhances the testability of the faults which are undetectable under conventional detection conditions (CDC) but may fail the circuit in some special function operations. The necessity and feasibility of the hazard-based detection condition is analyzed. Using the improved traditional stuck-at fault test generation tool, we have implemented an efficient HDC test generation for transition delay fault. Experimental results on ISCAS'89 benchmark circuits demonstrate that the proposed HDC test generation can improve the fault converage by an average of 3.64 % for conventional LOS test and an average of 4.6 % for conventional LOC test.

Steering symbolic execution to less traveled paths

Symbolic execution is a promising testing and analysis methodology. It systematically explores a program's execution space and can generate test cases with high coverage. One significant practical challenge for symbolic execution is how to effectively explore the enormous number of program paths in real-world programs. Various heuristics have been proposed for guiding symbolic execution, but they are generally inefficient and ad-hoc. In this paper, we introduce a novel, unified strategy to guide symbolic execution to less explored parts of a program. Our key idea is to exploit a specific type of path spectra, namely the length-n subpath program spectra , to systematically approximate full path information for guiding path exploration. In particular, we use frequency distributions of explored length- n subpaths to prioritize "less traveled" parts of the program to improve test coverage and error detection. We have implemented our general strategy in KLEE, a state-of-the-art symbolic execution engine. Evaluation results on the GNU Coreutils programs show that (1) varying the length n captures program-specific information and exhibits different degrees of effectiveness, and (2) our general approach outperforms traditional strategies in both coverage and error detection.