Unit testing a custom visual: how do you test update() and formatting settings?

Hi everyone,

I would like to hear how others structure automated tests for a custom visual built with the pbiviz tools. My current idea is to keep the rendering logic in plain functions that take a view model, so they can be tested without the Power BI host, and to test the update() path with a mocked data view.

// viewModel.ts - pure function, easy to test
export function toViewModel(categories: string[], values: number[]) {
  return categories.map((c, i) => ({ category: c, value: values[i] ?? 0 }));
}

// viewModel.spec.ts (Jest)
import { toViewModel } from "./viewModel";

test("pads missing values with zero", () => {
  expect(toViewModel(["a", "b"], [1])).toEqual([
    { category: "a", value: 1 },
    { category: "b", value: 0 },
  ]);
});

Questions:

• Which test setup do you use for the visual itself (Jest with jsdom, Karma, the powerbi-visuals-utils-testutils helpers), and what has been painful?
• How do you build realistic data views for tests, including empty data, many categories and null values?
• Do you test the formatting settings model (cards and slices) separately, and how do you check that the format pane maps to the capabilities file?

Thanks in advance.