errnolike

Errnolike is a term used in software engineering to describe values, constructs, or signaling patterns that imitate errno-style error reporting without invoking a true system error. In practice, errnolike data encodes an error code and an accompanying message, and is carried as part of normal program flow, such as in return values, result objects, or mock responses. The idea is to simulate error conditions in a controlled, deterministic way, enabling thorough testing of error handling paths and interoperability between components or languages that differ in their error conventions.

Key characteristics include a defined mapping between numeric codes and human-readable messages; portability across languages; and the absence of a process- or thread-wide fault when the error is produced. Errnolike constructs are commonly used in unit tests and integration tests, in mock servers or API fakes, and in cross-language bindings where one side uses errno-like signaling while the other uses exceptions or result types.

In practice, an errnolike signal may appear as a negative return code alongside a separate error context, a structured object with fields like error_code and error_message, or a JSON payload that communicates the failure reason. It is distinct from real errno usage in that it is designed for testing or mocking rather than for actual system errors.

See also: errno, error handling, mock objects, test doubles.