Structural testing is a type of testing that measures its effectiveness by tracking which lines of code were executed by the tests. Structural testing, also known as white-box testing or glass-box testing, is based on the internal structure, design, or implementation of the software. Structural testing aims to verify that the software meets the specified quality attributes, such as performance, security, reliability, or maintainability, by exercising the code paths, branches, statements, conditions, or data flows. Structural testing uses various coverage metrics, such as function coverage, line coverage, branch coverage, or statement coverage, to determine how much of the code has been tested and to identify any untested or unreachable parts of the code. Structural testing can be applied at any level of testing, such as unit testing, integration testing, system testing, or acceptance testing, but it is more commonly used at lower levels, where the testers have access to the source code.

The other options are not correct because they are not types of testing that measure their effectiveness by tracking which lines of code were executed by the tests. Acceptance testing is a type of testing that verifies that the software meets the acceptance criteria and the user requirements. Acceptance testing is usually performed by the end-users or customers, who may not have access to the source code or the technical details of the software. Acceptance testing is more concerned with the functionality, usability, or suitability of the software, rather than its internal structure or implementation. Integration testing is a type of testing that verifies that the software components or subsystems work together as expected. Integration testing is usually performed by the developers or testers, who may use both structural and functional testing techniques to check the interfaces, interactions, or dependencies between the components or subsystems. Integration testing is more concerned with the integration logic, data flow, or communication of the software, rather than its individual lines of code. Exploratory testing is a type of testing that involves simultaneous learning, test design, and test execution. Exploratory testing is usually performed by the testers, who use their creativity, intuition, or experience to explore the software and discover any defects, risks, or opportunities for improvement. Exploratory testing is more concerned with the behavior, quality, or value of the software, rather than its internal structure or implementation. References = ISTQB Certified Tester Foundation Level (CTFL) v4.0 syllabus, Chapter 4: Test Techniques, Section 4.3: Structural Testing Techniques, Pages 51-54; Chapter 1: Fundamentals of Testing, Section 1.4: Testing Throughout the Software Development Lifecycle, Pages 11-13; Chapter 3: Static Testing, Section 3.4: Exploratory Testing, Pages 40-41.