Latest Oct 29, 2024 Real CTFL_Syll_4.0 Exam Dumps Questions Valid CTFL_Syll_4.0 Dumps PDF [Q22-Q45]

The decision table provides conditions and corresponding actions. For C2:
* The user is logged in (Yes).
* The user is not authorized to view the profile (No).
* The correct action should be not to display the profile (No) and to display an error message (Yes).
This matches the actions listed for C2, making it the correct condition with the proper actions.

Explanation
A test task that usually occurs during test implementation is to make sure the planned test environment is ready to be delivered. The test environment is the hardware and software configuration on which the tests are executed, and it should be as close as possible to the production environment where the software system will operate. The test environment should be planned, prepared, and verified before the test execution, to ensure that the test conditions, the test data, the test tools, and the test interfaces are available and functional. The other options are not test tasks that usually occur during test implementation, but rather test tasks that occur during other test activities, such as:
Find, analyze, and remove the causes of the failures highlighted by the tests: This is a test task that usually occurs during test analysis and design, which is the activity of analyzing the test basis, designing the test cases, and identifying the test data. During this activity, the testers can use techniques such as root cause analysis, defect prevention, or defect analysis, to find, analyze, and remove the causes of the failures highlighted by the previous tests, and to prevent or reduce the occurrence of similar failures in the future tests.
Archive the testware for use in future test projects: This is a test task that usually occurs during test closure, which is the activity of finalizing and reporting the test results, evaluating the test process, and identifying the test improvement actions. During this activity, the testers can archive the testware, which are the test artifacts produced during the testing process, such as the test plan, the test cases, the test data, the test results, the defect reports, etc., for use in future test projects, such as regression testing, maintenance testing, or reuse testing.
Gather the metrics that are used to guide the test project: This is a test task that usually occurs during test monitoring and control, which is the activity of tracking and reviewing the test progress, status, and quality, and taking corrective actions when necessary. During this activity, the testers can gather the metrics, which are the measurements of the testing process, such as the test coverage, the defect density, the test effort, the test duration, etc., that are used to guide the test project, such as planning, estimating, scheduling, reporting, or improving the testing process. References: ISTQB Certified Tester Foundation Level (CTFL) v4.0 sources and documents:
ISTQB Certified Tester Foundation Level Syllabus v4.0, Chapter 2.1.1, Test Planning1 ISTQB Certified Tester Foundation Level Syllabus v4.0, Chapter 2.1.2, Test Monitoring and Control1 ISTQB Certified Tester Foundation Level Syllabus v4.0, Chapter 2.1.3, Test Analysis and Design1 ISTQB Certified Tester Foundation Level Syllabus v4.0, Chapter 2.1.4, Test Implementation1 ISTQB Certified Tester Foundation Level Syllabus v4.0, Chapter 2.1.5, Test Execution1 ISTQB Certified Tester Foundation Level Syllabus v4.0, Chapter 2.1.6, Test Closure1 ISTQB Glossary of Testing Terms v4.0, Test Environment, Test Condition, Test Data, Test Tool, Test Interface, Failure, Root Cause Analysis, Defect Prevention, Defect Analysis, Testware, Regression Testing, Maintenance Testing, Reuse Testing, Test Coverage, Defect Density, Test Effort, Test Duration2

This answer is correct because configuration management is a process of establishing and maintaining consistency of a product’s performance, functional, and physical attributes with its requirements, design, and operational information throughout its life. Configuration management helps ensure that all relevant project documentation and software items are uniquely identified in all their versions and therefore can be unambiguously referenced in test documentation. This supports testing by providing traceability, consistency, and control over the test artifacts and the software under test. Reference: : ISTQB Glossary of Testing Terms v4.0, : ISTQB Foundation Level Syllabus v4.0, Section 2.2.2.2

When a document management system is decommissioned, maintenance testing must include data migration testing to ensure that all documents are correctly transferred to a state archive, meeting legal requirements for long-term storage. This process verifies that data integrity is maintained during migration.
References:
* ISTQB CTFL Syllabus 4.0, Chapter 2.3, page 29: Maintenance Testing and Data Migration

Acceptance criteria for user stories are crucial in defining the specific requirements that a piece of software must meet to be accepted by the user or stakeholder. These criteria often include data definitions such as format, allowed values, and default values, ensuring that the software behaves correctly with the expected data inputs.
Option A is incorrect because user acceptance tests are not usually automated; they are often conducted manually by end-users. Option C is incorrect because acceptance criteria should cover both positive and negative scenarios to ensure comprehensive testing. Option D is incorrect because tests derived from acceptance criteria can indeed be included in the testing quadrants, particularly in the quadrant related to business-facing tests that critique the product.

Exploratory testing is an experience-based testing technique where test design and test execution occur simultaneously. It is characterized by the tester actively exploring the application, using their intuition and experience to uncover defects. Exploratory testing sessions are often guided by test charters, which are brief documents outlining the test objectives, scope, and areas to be explored during the session.
These test charters provide a flexible framework that directs the tester’s exploration without being overly prescriptive, allowing testers to adapt and investigate new areas as they uncover issues. This approach is particularly useful in dynamic and complex systems where predefined test cases might not cover all scenarios.
References:
* The official ISTQB CTFL syllabus explains the structure and benefits of exploratory testing, highlighting how test charters guide the testing process while allowing for flexibility and adaptability in identifying defects.

Test-driven development is not an example of a typical generic skill required for testing, but rather an example of a specific technical skill or a development practice that may or may not be relevant for testing, depending on the context and the objectives of the testing activities. Test-driven development is an approach to software development and testing, in which the developers write automated unit tests before writing the source code, and then refactor the code until the tests pass. Test-driven development can help to improve the quality, the design, and the maintainability of the code, as well as to provide fast feedback and guidance for the developers. However, test-driven development is not a skill that is generally expected or needed for testers, especially for testers who are not involved in unit testing or who do not have access to the source code. The other options are examples of typical generic skills required for testing, which are skills that are applicable and beneficial for testing in any context or situation, regardless of the specific testing techniques, tools, or methods used. The typical generic skills required for testing include:
* Be able to use test management tools and defect tracking tools: These are tools that help testers to plan, organize, monitor, and control the testing activities and resources, as well as to record, track, analyze, and resolve the defects detected during testing. These tools can improve the efficiency, the effectiveness, and the communication of the testing process, as well as to provide traceability, metrics, and reports for the testing outcomes.
* Be able to communicate defects and failures to developers as objectively as possible: This is a skill that involves the ability to report and describe the defects and failures found during testing in a clear, concise, accurate, and unbiased manner, using relevant information, evidence, and terminology, without making assumptions, judgments, or accusations. This skill can facilitate the collaboration, the understanding, and the resolution of the defects and failures between the testers and the developers, as well as to prevent conflicts, misunderstandings, or blame games.
* Possess the necessary social skills that support effective teamwork: These are skills that involve the ability to interact, cooperate, and coordinate with other people involved in or affected by the testing activities, such as the test manager, the test team, the project manager, the developers, the customers, the users, etc. These skills can include communication, negotiation, leadership, motivation, feedback, conflict resolution, etc. These skills can enhance the quality, the productivity, and the satisfaction of the testing process, as well as to foster a positive and constructive testing culture. References: ISTQB Certified Tester Foundation Level (CTFL) v4.0 sources and documents:
* ISTQB Certified Tester Foundation Level Syllabus v4.0, Chapter 1.1.1, Testing and the Software Development Lifecycle
* ISTQB Certified Tester Foundation Level Syllabus v4.0, Chapter 1.1.2, Testing and Quality
* ISTQB Certified Tester Foundation Level Syllabus v4.0, Chapter 1.2.1, Testing Principles
* ISTQB Certified Tester Foundation Level Syllabus v4.0, Chapter 1.2.2, Testing Policies, Strategies, and Test Approaches
* ISTQB Glossary of Testing Terms v4.0, Test-driven Development, Test Management Tool, Defect Tracking Tool, Defect Report, Failure, Social Skill2

Explanation
This answer is correct because the test procedures of all test cases that have been executed are not a typical content of a test completion report for a test project. A test completion report is a document that summarizes the test activities and results at the end of a test project. It usually includes information such as the test objectives, scope, approach, resources, schedule, results, deviations, issues, risks, lessons learned, and recommendations for improvement. The test procedures of all test cases that have been executed are part of the test documentation, but they are not relevant for the test completion report, as they do not provide a high-level overview of the test project outcomes and performance. References: ISTQB Foundation Level Syllabus v4.0, Section 2.5.3.2

Failures can be caused by defects, but also by environmental conditions. A failure is an event in which the software system does not perform a required function or performs a function incorrectly, according to the expected behavior. A defect is a flaw in the software system or a deviation from the requirements or the specifications, that may cause a failure. However, not all failures are caused by defects, as some failures may be caused by environmental conditions, such as hardware malfunctions, network interruptions, power outages, incompatible configurations, etc. Environmental conditions are factors that affect the operation of the software system, but are not part of the software system itself. The other statements are false, because:
A defect does not always produce a failure, while a bug always produces a failure. This statement is false, because a defect may or may not produce a failure, depending on the inputs, the outputs, the states, or the scenarios of the software system, and a bug is just another term for a defect, so it has the same possibility of producing a failure as a defect. For example, a defect in a rarely used feature or a hidden branch of the code may never produce a failure, while a defect in a frequently used feature or a critical path of the code may produce a failure often. A bug is not a different concept from a defect, but rather a synonym or a colloquial term for a defect, so it has the same definition and implications as a defect.
A defect may cause a failure which, when occurring, always causes an error. This statement is false, because an error is not a consequence of a failure, but rather a cause of a defect. An error is a human action or a mistake that produces a defect in the software system, such as a typo, a logic flaw, a requirement misunderstanding, etc. An error is not observable in the software system, but rather in the human mind or the human work products, such as the code, the design, the documentation, etc. A failure is not a cause of an error, but rather a result of a defect, which is a result of an error. For example, an error in the code may cause a defect in the software system, which may cause a failure in the software behavior.
Bugs are defects found during component testing, while failures are defects found at higher test levels. This statement is false, because bugs and failures are not different types of defects, but rather different terms for defects and their manifestations. As mentioned before, bugs are just another word for defects, and failures are the events in which the software system does not perform as expected due to defects. Bugs and failures can be found at any test level, not only at component testing or higher test levels. Test levels are the stages of testing that correspond to the levels of integration of the software system, such as component testing, integration testing, system testing, and acceptance testing. Defects and failures can occur and be detected at any test level, depending on the test objectives, the test basis, the test techniques, and the test environment. Reference: ISTQB Certified Tester Foundation Level (CTFL) v4.0 sources and documents:
ISTQB® Certified Tester Foundation Level Syllabus v4.0, Chapter 1.1.2, Testing and Quality1 ISTQB® Certified Tester Foundation Level Syllabus v4.0, Chapter 1.2.1, Testing Principles1 ISTQB® Certified Tester Foundation Level Syllabus v4.0, Chapter 1.3.1, Testing in Software Development Lifecycles1 ISTQB® Glossary of Testing Terms v4.0, Failure, Defect, Bug, Environmental Condition, Error, Test Level2

One of the typical potential risks associated with using test automation tools is the underestimation of the effort required to maintain test scripts. While test automation can reduce test execution times and provide more consistent and repeatable tests compared to manual testing, maintaining test scripts can be labor-intensive and often requires significant effort. Changes in the application under test can lead to frequent updates in the test scripts to keep them functional and relevant.
References:
* ISTQB CTFL Syllabus V4.0, Section 6.2 on the benefits and risks of test automation tools
* The syllabus outlines that while automation can improve efficiency, it also introduces maintenance challenges.

ATDD stands for Acceptance Test-Driven Development, which is a collaborative approach to software development and testing, in which the acceptance criteria of a user story are defined and automated as executable tests before the implementation of the software system. ATDD tests are usually written in a Given-When-Then format, which describes the preconditions, the actions, and the expected outcomes of a test scenario. ATDD tests are intended to verify that the software system meets the expectations and the needs of the users and the stakeholders, as well as to provide feedback and guidance for the developers and the testers. Based on the given information, the ATDD test that is most likely to be written first is the one that corresponds to option B, which is:
Given the logged-in user is on the Change Password page When the user enters the correct current password, enters a valid new password (different from the last 5 passwords), and presses the Change Password button Then the user receives an email confirming that the password has been successfully changed This ATDD test is most likely to be written first, because it covers the main functionality and the happy path of the user story, as well as the most important acceptance criterion [a]. It also verifies that the user can change the password with a valid new password that meets the criteria related to the length, the type of characters, and the history of the passwords, as specified in the acceptance criterion [c]. The other options are not likely to be written first, because they either cover less critical or less frequent scenarios, such as entering a wrong current password [d] or an invalid new password [e], or they are not related to the user story or the acceptance criteria at all, such as submitting a purchase order [d]. Reference: ISTQB Certified Tester Foundation Level (CTFL) v4.0 sources and documents:
ISTQB® Certified Tester Foundation Level Syllabus v4.0, Chapter 1.3.1, Testing in Software Development Lifecycles1 ISTQB® Glossary of Testing Terms v4.0, Acceptance Test-Driven Development, User Story, Acceptance Criterion, Given-When-Then2

Dynamic testing requires the execution of the software to evaluate its behavior and performance. In contrast, static testing involves examining the software’s code, design, and documentation without executing the software. This makes static testing applicable to non-executable work products such as requirement documents, design documents, and source code.

The V-model is a software development life cycle model that defines four test levels that correspond to four development phases: component (unit) testing with component design, integration testing with architectural design, system testing with system requirements, and acceptance testing with user requirements. The V-model emphasizes the importance of verifying and validating each phase of development with a corresponding level of testing, and ensuring that the test objectives, test basis, and test artifacts are aligned and consistent across the test levels. Therefore, an organization that wants to follow the V-model cannot do away with integration testing, as it would break the symmetry and completeness of the V-model, and compromise the quality and reliability of the software or system under test. Integration testing is a test level that aims to test the interactions and interfaces between components or subsystems, and to detect any defects or inconsistencies that may arise from the integration of different parts of the software or system. Integration testing is essential for ensuring the functionality, performance, and compatibility of the software or system as a whole, and for identifying and resolving any integration issues early in the development process. Skipping integration testing would increase the risk of finding serious defects later in the test process, or worse, in the production environment, which would be more costly and difficult to fix, and could damage the reputation and credibility of the organization. Therefore, the correct answer is D.
The other options are incorrect because:
A) It is not allowed as organizations can decide on the test levels to do depending on the context of the system under test. While it is true that the choice and scope of test levels may vary depending on the context of the system under test, such as the size, complexity, criticality, and risk level of the system, the organization cannot simply ignore or skip a test level that is defined and required by the chosen software development life cycle model. The organization must follow the principles and guidelines of the software development life cycle model, and ensure that the test levels are consistent and coherent with the development phases. If the organization wants to have more flexibility and adaptability in choosing the test levels, it should consider using a different software development life cycle model, such as an agile or iterative model, that allows for more dynamic and incremental testing approaches.
B) It is not allowed because integration testing is not an important test level and can be dispensed with. This statement is false and misleading, as integration testing is a very important test level that cannot be dispensed with. Integration testing is vital for testing the interactions and interfaces between components or subsystems, and for ensuring the functionality, performance, and compatibility of the software or system as a whole. Integration testing can reveal defects or inconsistencies that may not be detected by component (unit) testing alone, such as interface errors, data flow errors, integration logic errors, or performance degradation. Integration testing can also help to verify and validate the architectural design and the integration strategy of the software or system, and to ensure that the software or system meets the specified and expected quality attributes, such as reliability, usability, security, and maintainability. Integration testing can also provide feedback and confidence to the developers and stakeholders about the progress and quality of the software or system development. Therefore, integration testing is a crucial and indispensable test level that should not be skipped or omitted.
C) It is not allowed because integration testing is a very important test level and ignoring it means definite poor product quality. This statement is partially true, as integration testing is a very important test level that should not be ignored, and skipping it could result in poor product quality. However, this statement is too strong and absolute, as it implies that integration testing is the only factor that determines the product quality, and that ignoring it would guarantee a poor product quality. This is not necessarily the case, as there may be other factors that affect the product quality, such as the quality of the requirements, design, code, and other test levels, the effectiveness and efficiency of the test techniques and tools, the competence and experience of the developers and testers, the availability and adequacy of the resources and environment, the management and communication of the project, and the expectations and satisfaction of the customers and users. Therefore, while integration testing is a very important test level that should not be skipped, it is not the only test level that matters, and skipping it does not necessarily mean definite poor product quality, but rather a higher risk and likelihood of poor product quality.
Reference = ISTQB Certified Tester Foundation Level Syllabus, Version 4.0, 2018, Section 2.3, pages 16-18; ISTQB Glossary of Testing Terms, Version 4.0, 2018, pages 38-39; ISTQB CTFL 4.0 – Sample Exam – Answers, Version 1.1, 2023, Question 104, page 36.

Static testing involves reviewing the code, requirements, and design documents without executing the code. It is effective in finding certain types of bugs that do not require the code to be run. One common example of such a bug is variables that are declared but not initialized. These issues can be detected through code inspections or static analysis tools, which can identify uninitialized variables, missing declarations, and other coding standard violations without the need to execute the code.

According to the ISTQB Glossary of Testing Terms, Version 4.0, 2018, page 18, a failure is “an event in which a component or system does not perform a required function within specified limits”. In this case, the calculator software does not perform the required function of calculating the correct result for 5+6 within the specified limits of accuracy and precision. Therefore, this is an example of a failure.
The other options are incorrect because:
* A mistake is “a human action that produces an incorrect result” (page 25). A mistake is not an event, but an action, and it may or may not lead to a failure. For example, a mistake could be a typo in the code, a wrong assumption in the design, or a misunderstanding of the requirement.
* A fault is “a defect in a component or system that can cause the component or system to fail to perform its required function” (page 16). A fault is not an event, but a defect, and it may or may not cause a failure. For example, a fault could be a logical error in the code, a missing specification in the design, or a contradiction in the requirement.
* An error is “the difference between a computed, observed, or measured value or condition and the true, specified, or theoretically correct value or condition” (page 15). An error is not an event, but a difference, and it may or may not result in a failure. For example, an error could be a rounding error in the calculation, a measurement error in the observation, or a deviation error in the condition.
References = ISTQB Glossary of Testing Terms, Version 4.0, 2018, pages 15-18, 25; ISTQB CTFL 4.0 – Sample Exam – Answers, Version 1.1, 2023, Question 96, page 34.

* Looking for defects in a system does not require ignoring system details, but rather paying attention to them and understanding how they affect the system’s quality, functionality, and usability. Ignoring system details could lead to missing important defects or testing irrelevant aspects of the system.
* Identifying defects may be perceived as criticism against product, especially by the developers or stakeholders who are invested in the product’s success. However, identifying defects is not meant to be a personal attack, but rather a constructive feedback that helps to improve the product and ensure its alignment with the requirements and expectations of the users and clients.
* Looking for defects in system requires professional pessimism and curiosity, as testers need to anticipate and explore the possible ways that the system could fail, malfunction, or behave unexpectedly.
Professional pessimism means being skeptical and critical of the system’s quality and reliability, while curiosity means being eager and interested in finding out the root causes and consequences of the defects.
* Testing is often seen as a destructive activity instead of constructive activity, as it involves finding and reporting the flaws and weaknesses of the system, rather than creating or enhancing it. However, testing is actually a constructive activity, as it contributes to the system’s improvement, verification, validation, and optimization, and ultimately to the delivery of a high-quality product that meets the needs and expectations of the users and clients.

Independent of the software development lifecycle followed, it is a good practice to ensure that each test level (e.g., unit testing, integration testing, system testing) has clear and appropriate objectives. This ensures that the testing is focused and effective at each level. Other options either contradict good practices or are not applicable across all lifecycle models.
References:
* ISTQB CTFL Syllabus V4.0, Section 1.4.1 on test levels and objectives, emphasizing the importance of defining clear test objectives for each level of testing.

Option C correctly explains what is represented by the lines A, B and the axes X, Y in a testing metrics chart.
According to option D:
* X-axis represents Time
* Y-axis represents Count
* Line A represents Number of open bugs
* Line B represents Total number of executed tests
This information is essential in understanding and analyzing the testing metrics of a completed project.
References: ISTQB Certified Tester Foundation Level (CTFL) v4.0 Syllabus, Section 2.5.1, Page 35.

According to the ISTQB Certified Tester Foundation Level (CTFL) v4.0, the life cycle of a defect typically follows a sequence from its discovery to its closure. In the provided figure, it starts with S0 (New), moves to S1 (Assigned), then to S2 (Resolved), followed by S3 (Verified). If the defect is not fixed, it can be Re-opened (S5) and goes back for verification (S3). Once verified, it is Closed (S4). References: ISTQB Certified Tester Foundation Level (CTFL) v4.0 Syllabus, Section 1.4.3, Page 17.

Exploratory testing is an experience-based test technique in which testers dynamically design and execute tests based on their knowledge, intuition, and learning of the software system, without following predefined test scripts or test cases. Exploratory testing can be conducted following a session-based approach, which is a structured way of managing and measuring exploratory testing. In a session-based approach, the testers perform uninterrupted test sessions, usually lasting between 60 and 120 minutes, with a specific charter or goal, and document the issues detected, the test coverage achieved, and the time spent in session sheets. Session sheets are records of the test activities, results, and observations during a test session, which can be used for reporting, debriefing, and learning purposes. The other statements are false, because:
Exploratory testing is not a test technique in which testers explore the requirements specification to detect non testable requirements, but rather a test technique in which testers explore the software system to detect functional and non-functional defects, as well as to learn new information, risks, or opportunities. Non testable requirements are requirements that are ambiguous, incomplete, inconsistent, or not verifiable, which can affect the quality and effectiveness of the testing process. Non testable requirements can be detected by applying static testing techniques, such as reviews or inspections, to the requirements specification, before the software system is developed or tested.
Exploratory testing is not a test technique used by testers during informal code reviews to find defects by exploring the source code, but rather a test technique used by testers during dynamic testing to find defects by exploring the behavior and performance of the software system, without examining the source code. Informal code reviews are static testing techniques, in which the source code is analyzed by one or more reviewers, without following a formal process or using a checklist, to identify defects, violations, or improvements. Informal code reviews are usually performed by developers or peers, not by testers.
In exploratory testing, testers usually do not produce scripted tests and establish bidirectional traceability between these tests and the items of the test basis, but rather produce unscripted tests and adapt them based on the feedback and the findings of the testing process. Scripted tests are tests that are designed and documented in advance, with predefined inputs, outputs, and expected results, and are executed according to a test plan or a test procedure. Bidirectional traceability is the ability to trace both forward and backward the relationships between the items of the test basis, such as the requirements, the design, the risks, etc., and the test artifacts, such as the test cases, the test results, the defects, etc. Scripted tests and bidirectional traceability are usually associated with more formal and structured testing approaches, such as specification-based or structure-based test techniques, not with exploratory testing. Reference: ISTQB Certified Tester Foundation Level (CTFL) v4.0 sources and documents:
ISTQB® Certified Tester Foundation Level Syllabus v4.0, Chapter 2.2.3, Experience-based Test Design Techniques1 ISTQB® Glossary of Testing Terms v4.0, Exploratory Testing, Session-based Testing, Session Sheet, Non Testable Requirement, Static Testing, Informal Review, Dynamic Testing, Scripted Testing, Bidirectional Traceability2

This answer is correct because shift-left in testing is an approach that aims to perform testing activities as early as possible in the software development lifecycle, in order to find and fix defects faster and cheaper, and to improve the quality of the software product. Continuous integration is a practice that supports shift-left in testing, as it involves integrating and testing the software components frequently, usually several times a day, using automated tools and processes. Continuous integration can reduce the time between the introduction of a defect and its detection, thereby reducing the cost to fix it and the risk of accumulating defects that could affect the functionality or performance of the software product. References: ISTQB Foundation Level Syllabus v4.0, Section 3.1.1.3, Section 3.2.1.3

A pilot project is a small-scale experiment or trial that is conducted to evaluate the feasibility, effectiveness, and suitability of a test automation tool before implementing it on a larger scale1.
The objectives of a pilot project may vary depending on the context and scope of the test automation initiative, but some common ones are2:
To get familiar with the functionality and options of the tool
To check how the tool fits to the existing test processes and environment To assess the benefits and challenges of using the tool To decide upon standards and guidelines for tool implementation and usage To estimate the costs and resources required for tool deployment and maintenance Therefore, option C is not a valid objective of a pilot project, as it is not necessary to train all testers on using the tool at this stage. Training all testers on using the tool would be more appropriate after the tool has been selected and approved for full-scale implementation, and after the standards and guidelines have been established. Training all testers on using the tool during the pilot project would be inefficient, costly, and premature, as the tool may not be suitable or effective for the intended purpose, or may be replaced by another tool later.
Reference:
1: ISTQB Certified Tester Foundation Level Syllabus 2018, Version 4.0, p. 82
2: ISTQB Certified Tester Foundation Level Syllabus 2018, Version 4.0, p. 83
3: ISTQB Certified Tester Foundation Level Syllabus 2018, Version 4.0, p. 84
4: ISTQB Certified Tester Foundation Level Syllabus 2018, Version 4.0, p. 85

Failures can be caused by defects, but also by environmental conditions. A failure is an event in which the software system does not perform a required function or performs a function incorrectly, according to the expected behavior. A defect is a flaw in the software system or a deviation from the requirements or the specifications, that may cause a failure. However, not all failures are caused by defects, as some failures may be caused by environmental conditions, such as hardware malfunctions, network interruptions, power outages, incompatible configurations, etc. Environmental conditions are factors that affect the operation of the software system, but are not part of the software system itself. The other statements are false, because:
* A defect does not always produce a failure, while a bug always produces a failure. This statement is false, because a defect may or may not produce a failure, depending on the inputs, the outputs, the states, or the scenarios of the software system, and a bug is just another term for a defect, so it has the
* same possibility of producing a failure as a defect. For example, a defect in a rarely used feature or a hidden branch of the code may never produce a failure, while a defect in a frequently used feature or a critical path of the code may produce a failure often. A bug is not a different concept from a defect, but rather a synonym or a colloquial term for a defect, so it has the same definition and implications as a defect.
* A defect may cause a failure which, when occurring, always causes an error. This statement is false, because an error is not a consequence of a failure, but rather a cause of a defect. An error is a human action or a mistake that produces a defect in the software system, such as a typo, a logic flaw, a requirement misunderstanding, etc. An error is not observable in the software system, but rather in the human mind or the human work products, such as the code, the design, the documentation, etc. A failure is not a cause of an error, but rather a result of a defect, which is a result of an error. For example, an error in the code may cause a defect in the software system, which may cause a failure in the software behavior.
* Bugs are defects found during component testing, while failures are defects found at higher test levels.
This statement is false, because bugs and failures are not different types of defects, but rather different terms for defects and their manifestations. As mentioned before, bugs are just another word for defects, and failures are the events in which the software system does not perform as expected due to defects.
Bugs and failures can be found at any test level, not only at component testing or higher test levels. Test levels are the stages of testing that correspond to the levels of integration of the software system, such as component testing, integration testing, system testing, and acceptance testing. Defects and failures can occur and be detected at any test level, depending on the test objectives, the test basis, the test techniques, and the test environment. References: ISTQB Certified Tester Foundation Level (CTFL) v4.0 sources and documents:
* ISTQB Certified Tester Foundation Level Syllabus v4.0, Chapter 1.1.2, Testing and Quality1
* ISTQB Certified Tester Foundation Level Syllabus v4.0, Chapter 1.2.1, Testing Principles1
* ISTQB Certified Tester Foundation Level Syllabus v4.0, Chapter 1.3.1, Testing in Software Development Lifecycles1
* ISTQB Glossary of Testing Terms v4.0, Failure, Defect, Bug, Environmental Condition, Error, Test Level2

Quality Assurance (QA) and Quality Control (QC) are both essential aspects of a comprehensive quality management system but they serve different purposes:
* Quality Assurance (QA): QA is a process-oriented approach that focuses on preventing defects by improving the processes used to develop and test products. It involves setting up processes, methodologies, and standards to ensure that the product meets quality requirements.
* Quality Control (QC): QC is a product-oriented approach that focuses on identifying defects in the final products. It involves activities such as inspection, testing, and review to ensure that the product meets the specified requirements and standards.
Thus, the main difference is that QA is process-oriented and preventive, while QC is product-oriented and corrective.