Battle-for-Tismo/tests/growth_test.js

import { TestCase } from "./framework/test_case.js";
import { smallState } from "./framework/helpers.js";
import { ECONOMY } from "../shared/data.js";
import { HOURS_PER_DAY } from "../shared/game_state/constants.js";
import { parseKey } from "../shared/hex.js";

// Natural GDP-per-capita growth: a constant daily amount measured from each
// tile's opening figure, so the relative growth rate tapers over the years.
export class GdpGrowthTest extends TestCase {
  firstBaseline(state) {
    const k = state.tileGdpBaseline.keys().next().value;
    return { k, baseline: state.tileGdpBaseline.get(k), coords: parseKey(k) };
  }

  test_a_day_adds_a_constant_share_of_the_opening_figure() {
    const state = smallState();
    const { k, baseline, coords } = this.firstBaseline(state);
    this.assertTrue(baseline > 0, "the tile has an opening GDP per capita");
    const opening = state.getTileGdpPerCapita(coords);
    this.assertApprox(opening, baseline, 1e-9, "day zero is the baseline");
    for (let i = 0; i < HOURS_PER_DAY; i++) state.tickHour();
    const dayOne = state.getTileGdpPerCapita(coords);
    const step = baseline * ECONOMY.naturalGdpGrowthPerDay;
    this.assertApprox(dayOne - opening, step, 1e-6, "one day adds one step");
    // Thirty more days add exactly thirty more steps: the amount is constant.
    state.totalHours = 31 * HOURS_PER_DAY;
    state._gdpPerCapitaCache.clear();
    const dayThirtyOne = state.getTileGdpPerCapita(coords);
    this.assertApprox(dayThirtyOne - dayOne, 30 * step, 1e-6, "the daily amount never grows");
    this.assertEqual(k, state.tileGdpBaseline.keys().next().value, "the baseline never moves");
  }

  test_the_relative_growth_rate_falls_as_the_tile_grows() {
    const state = smallState();
    const { baseline, coords } = this.firstBaseline(state);
    const step = baseline * ECONOMY.naturalGdpGrowthPerDay;
    const earlyRate = step / baseline;
    state.totalHours = 366 * HOURS_PER_DAY;
    state._gdpPerCapitaCache.clear();
    const value = state.getTileGdpPerCapita(coords);
    // The same constant step, a year later, is a smaller share of a bigger
    // figure: the relative rate has fallen.
    const laterRate = step / (value - step);
    this.assertTrue(value > baseline, "the tile is richer than it began");
    this.assertTrue(laterRate < earlyRate, "the same gain is now a smaller share");
  }

  test_growth_is_measured_from_january_2000_in_the_first_year() {
    const state = smallState();
    const growth = state.viewerStats(0).growth;
    this.assertNotNull(growth, "the viewer carries growth figures");
    this.assertTrue(growth.sinceStart, "the first year measures from January 2000");
    this.assertApprox(growth.gdpPerCapita, 0, 1e-9, "nothing has grown yet");
    for (let i = 0; i < HOURS_PER_DAY; i++) state.tickHour();
    const after = state.viewerStats(0).growth;
    this.assertTrue(after.sinceStart, "still the first year");
    this.assertTrue(after.gdpPerCapita > 0, "a day of growth is reported");
    this.assertTrue(after.gdp > after.gdpPerCapita, "GDP also carries population growth");
  }

  test_growth_becomes_year_on_year_after_the_first_year() {
    const state = smallState();
    const current = state._monthIndexOf(state.totalHours);
    // A year on, the same month last year is the baseline. Halve it so the
    // comparison has an unmistakable answer.
    const past = state._captureMonthlyStats();
    for (const entry of past) {
      entry.population = Math.floor(entry.population / 2);
      entry.gdp = entry.gdp / 2;
      entry.gdpPerCapita = entry.gdpPerCapita / 2;
    }
    state._monthIndexNow = current;
    state._monthStartHistory = [
      { index: current - 13, stats: past },
      { index: current - 12, stats: past },
      { index: current, stats: state._captureMonthlyStats() },
    ];
    const growth = state._growthRates(0);
    this.assertFalse(growth.sinceStart, "with a year of history it is year on year");
    this.assertApprox(growth.population, 1, 1e-6, "the population doubled");
    this.assertApprox(growth.gdp, 1, 1e-6, "the GDP doubled");
  }

  test_the_snapshot_ships_the_growth_baseline_once() {
    const state = smallState();
    const first = state.snapshot(0);
    this.assertSize(
      first.gdpBaseline,
      state.tileGdpBaseline.size,
      "every baseline tile travels"
    );
    this.assertNotNull(first.viewerStats.growth, "the viewer's growth travels too");
    // The version never moves, so the delta wire drops the baseline afterwards.
    this.assertEqual(first.versions.gdpBaseline, 0, "the baseline version is static");
  }
}