verify

name	verify
description	Verify fac (terminal text editor) changes by driving the TUI in a pty with pexpect + pyte. Use after changing editor behavior, rendering, input handling, or LSP features.

Verifying fac end-to-end

fac is a TUI; verification means driving it in a pty and inspecting the rendered screen. No tmux on this machine — use Python pexpect (pty driver) plus pyte (virtual terminal that interprets the ANSI stream).

Setup (once per session)

cd <scratchpad>
python3 -m venv venv && ./venv/bin/pip install pexpect pyte

Driver pattern

import pexpect, pyte, time
screen = pyte.Screen(80, 24); stream = pyte.Stream(screen)
child = pexpect.spawn("/abs/path/to/fac", ["file.txt"], dimensions=(24, 80),
                      env={**os.environ, "TERM": "xterm-256color"})
def drain(wait=0.4):   # read fac's output into the virtual terminal
    end = time.time() + wait
    while time.time() < end:
        try: stream.feed(child.read_nonblocking(65536, 0.1).decode("utf-8","replace"))
        except pexpect.TIMEOUT: pass
        except pexpect.EOF: break
child.send("x"); drain()          # type; then inspect screen.display

Screen geometry gotchas

• Row 0 of screen.display is the tab bar; buffer line N is display index N (1-based line lands on 0-based index N). Status bar = last row.
• Line-number gutter is 6 columns (LINE_NUMBER_WIDTH=5 + space): buffer column c (1-based) is at screen col 5 + c (0-based).
• Colors: screen.buffer[row][col].fg — e.g. ghost text is brightblack (ESC[90m), normal text default. pyte does not track dim (SGR 2).

Key bytes

ctrl-e \x05, ctrl-s \x13, ctrl-q \x11, ctrl-z \x1a, tab \t, enter \r, esc \x1b, backspace \x7f, down \x1b[B, right \x1b[C, shift-home \x1b[1;2H, alt-r \x1br, ctrl-space \x00 (NUL).

Proving edits are real

Send ctrl-s then read the file from disk — screen checks can lie about buffer state; the saved file can't.

LSP scenarios

• clangd is installed; open a .c file and fac auto-starts it (verify with pgrep -a clangd). Allow ~3s init before typing; allow ~2s drain after a request before asserting.
• Use a .txt file to guarantee NO LSP server (isolates non-LSP paths).
• To prove a completion came from LSP, use a symbol that appears nowhere in the file text (e.g. printf with only the #include present).
• Document sync to servers is debounced 500ms (document_sync_module); features that need current text must force-flush (flush_pending_changes(..., .true.)) before requesting.
• References (alt-r) is a known-good callback-wired LSP feature — use it as a control when LSP plumbing seems broken.

Unit tests

Standalone programs in test/; compile against the .o/.mod files that make leaves in the repo root:

gfortran -O0 -g -fcheck=all -I. test/test_X.f90 src/.../dep1.o src/.../dep2.o -o /tmp/t && /tmp/t