Testing a Viewer

A plot is an ordinary function or object: it takes the run’s data and returns drawables (see Plots and Drawables). So it can be tested without a window, a screen or the gui extra, by giving it the data of a stored run and checking what it returns.

# tests/test_viz.py
from plesty.lib.monitor import Line, RunData

from power_viz import power      # the plot function of the viewer being tested


def test_power_draws_one_point_per_step():
    data = RunData("tests/runs/powerscan_20260925-101534")
    data.poll()                  # read the rows saved so far

    drawing = power(data)

    assert len(drawing) == 1
    assert isinstance(drawing[0], Line)
    assert list(drawing[0].x) == [500.0, 550.0, 600.0, 650.0, 700.0]

• RunData(run_folder) reads nothing yet; poll() reads every row saved so far and returns how many it read. In a viewer, Viz does this at each refresh.

• @viz.plot returns the function unchanged, so the test calls power(data) directly. For a Plot object, call plot.draw(data).

• Keep a small finished run in the module’s tests, made by running the experiment once on its simulated devices, so the test does not depend on a lab computer.

A viewer’s reads= function can be tested the same way: call it with a row and a Run, and check the fields it returns.