monkey-testing-pbt.ts

/*
 * This code snippet is an extract of a private codebase. Though it relies on many dependencies to
 * the rest of the codebase, I believe that the code carries enough intension so that one can get
 * the overall idea (see: https://blog.mathieueveillard.com/monkey-testing-et-property-based-testing-une-exploration)
 */

import fc from "fast-check";

const ALL_REDUCERS: HasName<Reducer<ApplicationState>>[] = [
  withName("selectPhotograph")(pickRandomIndex(getNumberOfPhotographs)(selectionReducers.selectPhotograph)),
  withName("selectPreviousPhotograph")(selectionReducers.selectPreviousPhotograph),
  withName("selectNextPhotograph")(selectionReducers.selectNextPhotograph),
  withName("selectLowerPhotograph")(selectionReducers.selectLowerPhotograph),
  withName("selectUpperPhotograph")(selectionReducers.selectUpperPhotograph),
  withName("selectFirstPhotograph")(selectionReducers.selectFirstPhotograph),
  withName("selectLastPhotograph")(selectionReducers.selectLastPhotograph),
  withName("resetSelection")(selectionReducers.resetSelection),
  withName("selectDeletedPhotograph")(pickRandomIndex(getNumberOfDeletedPhotographs)(trashBinSelectionReducers.selectDeletedPhotograph)),
  withName("selectPreviousDeletedPhotograph")(trashBinSelectionReducers.selectPreviousDeletedPhotograph),
  withName("selectNextDeletedPhotograph")(trashBinSelectionReducers.selectNextDeletedPhotograph),
  withName("selectFirstDeletedPhotograph")(trashBinSelectionReducers.selectFirstDeletedPhotograph),
  withName("selectLastDeletedPhotograph")(trashBinSelectionReducers.selectLastDeletedPhotograph),
  withName("resetDeletedPhotographsSelection")(trashBinSelectionReducers.resetDeletedPhotographsSelection),
  withName("moveDown")(photographReducers.moveDown),
  withName("moveUp")(photographReducers.moveUp),
  withName("moveToFirst")(photographReducers.moveToFirst),
  withName("moveToLast")(photographReducers.moveToLast),
  withName("deleteSelection")(photographReducers.deleteSelection),
  withName("cancel")(cancellationReducers.cancel),
  withName("restorePhotograph")(trashBinReducers.restorePhotograph),
  withName("zoomIn")(zoomReducers.zoomIn),
  withName("zoomOut")(zoomReducers.zoomOut),
  withName("zoomMin")(zoomReducers.zoomMin),
  withName("zoomMax")(zoomReducers.zoomMax),
  withName("resetZoom")(zoomReducers.resetZoom),
  withName("enterSlideshow")(focusReducers.enterSlideshow),
  withName("exitSlideshow")(focusReducers.exitSlideshow),
  withName("enterSlideshowAtIndex")(pickRandomIndex(getNumberOfPhotographs)(focusReducers.enterSlideshowAtIndex)),
  withName("toggleSlideshow")(focusReducers.toggleSlideshow),
  withName("toggleTrashBin")(focusReducers.toggleTrashBin),
];

describe("Monkey testing", () => {
  test("Random actions that preserve the overall number of photographs", () => {
    fc.assert(
      fc.property(
        fc.nat({ max: 10 }),
        fc.nat({ max: 10 }),
        (numberOfPhotographs, numberOfDeletedPhotographs) => {
          // GIVEN
          const state = mockState<ApplicationState>({
            photographs: arrayOfPhotographs(numberOfPhotographs),
            trashBin: arrayOfPhotographs(numberOfDeletedPhotographs),
            selection: "NO_INDEX",
            trashBinSelection: "NO_INDEX",
            cancellation: "NOTHING_TO_CANCEL",
            focus: "THUMBNAILS",
            zoom: 5,
          });
          const numberOfActions = 100;

          // WHEN
          const nextState = repeat<ApplicationState>(numberOfActions)(
            pickRandomReducer(ALL_REDUCERS)
          )(state);

          // THEN
          return (
            getNumberOfPhotographs(nextState) +
              getNumberOfDeletedPhotographs(nextState) ===
            getNumberOfPhotographs(state) + //
              getNumberOfDeletedPhotographs(state)
          );
        }
      )
    );
  });
});