Testing involves checking for both conformance to specified requirements and non-conformance to reasonable expectations (implicit requirements). A user would reasonably expect that an account with a zero balance is still a ‘valid account,’ and a failure in this case likely represents a defect. The tester’s duty is to report it so the project team can decide on its priority.

The scenario describes a very narrow test condition, which would lead to minimal test coverage. Coverage is a measure of the extent to which test cases exercise the software (e.g., requirement coverage, code coverage). Good testing aims for adequate coverage based on risk, and a single positive test for login critically lacks coverage for incorrect passwords, locked accounts, SQL injection, etc.

System testing is performed on a complete, integrated system to evaluate its compliance with specified requirements. Testing the ‘Add to Cart’ feature on the full e-commerce website, which involves the user interface, application logic, and database interactions, is a classic example of system functional testing.

The tester is choosing values at the edges of the input domain (0,1 and 50,51). Boundary Value Analysis (BVA) is a technique where test cases are designed based on boundary values. Valid boundaries are 1 and 50, and invalid boundaries are 0 and 51. The value 49 is a representative valid interior value often included with BVA.

Confirmation testing (or re-testing) is executed to confirm that a defect has been successfully fixed. This involves re-running the test that originally revealed the defect. The question also hints at regression testing (‘doesn’t break anything else’), but the primary focus described is verifying the specific fix, which is the core of confirmation testing.

The principle ‘Exhaustive testing is impossible’ states that testing everything (all combinations of inputs and preconditions) is not feasible. A complex integration flow has a vast number of potential states and data combinations. The team must use risk and priorities to select test cases, meaning some untested paths, like this one, can contain defects.

An Interface Specification (or API specification) is the correct test basis for testing an API. It defines the contract for how software components will interact, including endpoints, request/response formats, data types, and status codes. This document is essential for designing tests before any GUI or full implementation is complete.

State transition testing is used for systems that have defined states and transition between them based on events or conditions. Test cases are designed to exercise valid transitions (e.g., Green -> Yellow) and often to test for invalid ones (e.g., Green -> Red). The other options, while potentially testable, are not the focus of the state transition technique.

In the V-model, testing activities are planned in parallel with corresponding development stages. After system design is complete, the next development phase is component design. In parallel, the testing team should be reviewing the system design documents (from the *just completed* phase) to create system test conditions and cases. This embodies the ‘early testing’ principle.

Testing involves checking for both conformance to specified requirements and non-conformance to reasonable expectations (implicit requirements). A user would reasonably expect that an account with a zero balance is still a ‘valid account,’ and a failure in this case likely represents a defect. The tester’s duty is to report it so the project team can decide on its priority.0