Add automated test suite with BATS

[linuz90]

Why

lwt has no tests. As features grow (aliases, -yolo, agent integration), it's easy to break argument parsing, worktree path logic, or status detection silently.

Proposal

Use bats-core with --shell /bin/zsh so tests run in the same shell lwt uses.

What to test

• Utility functions: editor resolution, random branch names, .env copying, lockfile detection, merge/dirty/unpushed status detection
• Argument parsing: every command's flags, options, error cases
• Worktree operations: correct paths (../.worktrees/<project>/<branch>/), branch creation, auto-naming
• Dispatch: routing, aliases (a/s/ls/rm/rn), help output
• Doctor: dependency reporting

What to skip

• fzf interaction, editor/agent launching, real network calls — all mocked

Isolation

Each test creates a disposable git repo in /tmp. No side effects on real repos.

Structure

test/
  test_helper/
    bats-support/   # submodule
    bats-assert/    # submodule
    common.bash     # shared setup/teardown + mocks
  utils.bats        # start here — pure functions
  dispatch.bats
  add.bats
  list.bats
  remove.bats
  clean.bats
  rename.bats
  doctor.bats

Run

brew install bats-core
bats --shell /bin/zsh test/