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102 lines
3.9 KiB
Markdown
102 lines
3.9 KiB
Markdown
# Driving a CLI / TUI (tmux)
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Each scenario gets its own named tmux session (cleanup needs a deterministic
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name). Fix the size for deterministic capture; prefer the app's plain-text/inline
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mode if it has one.
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## The four-command recipe
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```bash
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tmux new-session -d -s <name> -x 200 -y 50 "<cmd> 2>/tmp/<name>-stderr.log"
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tmux send-keys -t <name> -l "literal text" # -l = no key-name parsing (paths, slashes)
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tmux send-keys -t <name> Enter
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tmux capture-pane -t <name> -p # -p = plain text; add -e only for styling
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```
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- `-x 200 -y 50` fixes the pane size so `capture-pane` output is deterministic
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run to run — a resized pane reflows text differently.
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- Always `-l` for user-typed strings; without it a literal path like
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`/foo/bar` gets parsed as arrow-key escapes instead of typed characters.
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- Redirect stderr to a file — panics, log lines, and debug probes land there,
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not in the pane, so they won't show up in a `capture-pane` snapshot at all.
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Kill any leftover session with the same name before starting a new one, so
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reruns don't attach to a stale process:
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```bash
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tmux kill-session -t <name> 2>/dev/null # idempotent: fine if nothing to kill
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```
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## Form fill: send-keys patterns
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`send-keys` parses keystrokes by name (`Enter`, `BTab`, `C-u`) unless you pass
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`-l` for literal text. A typical field-by-field fill mixes both:
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```bash
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tmux send-keys -t <name> "n" # tap a key to open the form
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sleep 1
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tmux send-keys -t <name> BTab # shift-tab back one field
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sleep 0.3
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tmux send-keys -t <name> C-u # clear the current line
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sleep 0.3
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tmux send-keys -t <name> -l "some/literal/path" # literal — no key parsing
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sleep 0.3
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tmux send-keys -t <name> Tab # forward to next field
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sleep 0.3
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tmux send-keys -t <name> -l "text the user would type"
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sleep 0.3
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tmux send-keys -t <name> Enter # submit
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```
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`sleep 0.3` between keys is usually enough; bump to 0.5–1.0s for field
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transitions where the UI re-renders.
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## Polling capture-pane for state
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Poll `capture-pane -p` for a state string and grep the **glyph or word**, not
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the color — `-p` drops ANSI styling by default (add `-e` only if you need
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styling), and colors are also just harder to grep reliably than a fixed
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glyph:
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```bash
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for i in $(seq 1 30); do
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pane=$(tmux capture-pane -t <name> -p)
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echo "$pane" | grep -q "state: processing" && break
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sleep 1
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done
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```
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TUIs commonly use a distinct glyph per state, e.g. a Braille spinner (`⠋`)
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while pending and an X mark (`✗`) on failure, with the glyph simply removed
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once reconciled. Grep for the glyph itself, not for a color code.
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## Two captures for optimistic UI
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Mirror the web sync/async pattern: capture the pane immediately after the
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triggering keypress, then again after a reconcile window. Without the
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immediate capture you can't tell "rendered then reconciled" from "never
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rendered":
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```bash
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tmux send-keys -t <name> -l "trigger the optimistic action"
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tmux send-keys -t <name> Enter
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echo "=== synchronous ===" ; tmux capture-pane -t <name> -p | grep -E "pending-glyph"
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sleep 6
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echo "=== reconciled ===" ; tmux capture-pane -t <name> -p | grep -E "pending-glyph" || echo "[no pending — reconciled]"
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```
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## Plain-text mode over the alt-screen buffer
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If the TUI has a flag that disables its alternate-screen buffer (a debug or
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plain-output mode), use it when launching under tmux. `capture-pane` then sees
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plain scrollback text instead of raw escape sequences from a full-screen
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redraw, which is much easier to grep.
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## Non-interactive CLIs don't need tmux
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If the surface under test is a one-shot command rather than an interactive
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session, skip tmux entirely — run the command and capture its stdout/stderr
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directly. The tmux machinery exists for interaction, not for driving a binary
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in general. Still run it against a real, freshly built instance, not a stale
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one left over from an earlier session.
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