Module mock 

MockTape — an in-memory tape simulation for unit testing.

Real tape hardware is not available in most CI environments, and even when it is, tests that touch a physical drive are slow and potentially destructive. MockTape lets the entire higher-level logic of tape-backup-lib be tested without any hardware.

Model

A real tape stores data as a sequence of tape files separated by filemarks. MockTape represents this as a Vec<Vec<u8>>, where each inner Vec<u8> holds the bytes of one tape file. The current position is tracked as a (file_index, byte_offset) pair.

Filemark behaviour

Reading returns Ok(0) (zero bytes) when the read cursor reaches the end of the current tape file, mirroring the Linux st driver. The filemark is auto-consumed: file_idx advances automatically, so the next read call immediately returns data from the following tape file. Do not call Tape::space_filemarks(1) between consecutive tape-file reads; that would skip one additional filemark.

Overwrite semantics

Writing at position (f, b) truncates the current tape file at offset b and removes all tape files that follow — mirroring the behaviour of a real tape, where the write head physically overwrites everything from the current position onwards. This means that rewinding and writing new data replaces everything that was there before.

Structs

MockTape

In-memory tape simulation. See the module documentation for the model and behavioural contract.