What signs indicate that a function or module has full test coverage?

Signs of completion and full coverage of a function or module by unit tests:

• Code coverage: all branches, conditions, and possible execution paths are tested.
• Boundary case testing: tests cover edge and unusual input data.
• Error testing: proper handling of exceptions and errors is verified.
• Repeatability: tests produce stable results upon repeated runs.
• Isolation: tests do not depend on external resources (files, network) or state.
• Documentation: tests are understandable and reflect functional requirements.

For example, for a division function, there should be tests for normal cases, division by zero (with exception thrown), and input data type checks.

Coverage tools (coverage.py) help visually assess which parts of the code are not covered by tests.