The principle of exhaustive testing (testing all possible combinations) is not feasible except for trivial cases. This is a fundamental concept in testing (ISTQB FL 1.2). While the other options highlight real concerns, the most direct and critical limitation of the phrase ‘all functional requirements must be tested’ is the impracticality of testing every possible scenario.

Static testing (like reviews or walkthroughs) of specifications early in the lifecycle helps identify defects before they are built into the code. Catching ambiguities in acceptance criteria during sprint planning prevents misinterpretation and subsequent bug injection, aligning with the shift-left principle (ISTQB FL 1.4.2).

While the fundamental test process is a lifecycle model for individual test activities, organizing the repository of test cases themselves is typically done by feature, component, or risk to maintain clear traceability to requirements. This is crucial for impact analysis and progress reporting (ISTQB FL 5.2.2).

A decision table lists all combinations of inputs (conditions) and their resulting outputs (actions). With two binary conditions (Login State: 2 options, Network: 2 options), the total number of combinations is 2 * 2 = 4. For example: (Logged In, Online), (Logged In, Offline), (Logged Out, Online), (Logged Out, Offline).

A production-like environment is a dedicated, controlled setting that closely mimics the final production environment in terms of hardware, software, network configuration, and other systems. It is used for system, system integration, and acceptance testing to provide high confidence before release (ISTQB FL 5.2.4).

The first step after observing a failure is to confirm it is a genuine, reproducible failure and not a false positive caused by a test data issue, environmental glitch, or mistaken expected result. Re-execution (sometimes a few times) is a standard initial check to avoid ‘noise’ in the defect tracking system (ISTQB FL 5.6.1).

Requirements coverage is a metric that measures the percentage of requirements that are addressed by test cases. The mandate ensures that the numerator (requirements covered by tests) includes all requirements, aiming for 100% requirements coverage, which is often critical in regulated industries (ISTQB FL 5.5.1).

A core principle of risk-based testing is to prioritize testing of high-risk items. This means testing them early (to find critical defects sooner) and often applying more thorough test techniques (like detailed input validation testing) to mitigate the identified risk effectively (ISTQB FL 1.4.2, 4.2).

In acceptance testing, the business stakeholders (e.g., product owner) are responsible for validation—confirming the software meets their needs and is fit for use. Professional testers often play a supporting role, helping to design, automate, and execute tests to enable efficient validation by the business (ISTQB FL 2.2.1).

The principle of exhaustive testing (testing all possible combinations) is not feasible except for trivial cases. This is a fundamental concept in testing (ISTQB FL 1.2). While the other options highlight real concerns, the most direct and critical limitation of the phrase ‘all functional requirements must be tested’ is the impracticality of testing every possible scenario.0