Battle-for-Tismo/tests/migration_test.js

import { TestCase } from "./framework/test_case.js";
import { smallState, cityOf } from "./framework/helpers.js";
import { key } from "../shared/hex.js";

export class MigrationTest extends TestCase {
  test_food_output_comes_from_the_land_not_the_headcount() {
    const state = smallState();
    const city = cityOf(state, 0);
    const before = state._regionProductionValue(city);
    // Pack many more people onto the same land: the harvest must not change.
    for (const coords of state.regionTiles(city)) {
      const k = key(coords.x, coords.y);
      state.tilePopulation.set(k, (state.tilePopulation.get(k) || 0) * 4 + 1);
    }
    state._gdpPerCapitaCache.clear();
    const after = state._regionProductionValue(city);
    this.assertApprox(after, before, 1e-6, "the land yields the same however many live on it");
  }

  test_regions_of_a_nation_open_with_equal_income_per_head() {
    const state = smallState();
    for (let civ = 0; civ < state.civilisations.length; civ++) {
      const cities = state.cities.filter((city) => city.civ === civ);
      if (cities.length < 2) continue;
      const perHead = cities.map((city) => {
        const economy = state.getCityEconomy(city);
        return economy.population > 0 ? economy.gdp / economy.population : 0;
      });
      const highest = Math.max(...perHead);
      const lowest = Math.min(...perHead);
      this.assertTrue(
        highest > 0 && (highest - lowest) / highest <= 0.02,
        `regions of civ ${civ} open level`
      );
    }
  }

  test_moving_people_conserves_the_total() {
    const state = smallState();
    const cities = state.cities.filter((city) => city.civ === 0);
    this.assertGreaterOrEqual(cities.length, 2, "the fixture has two regions");
    const from = cities[0];
    const to = cities[1];
    const fromBefore = state.regionPopulation(from);
    const toBefore = state.regionPopulation(to);
    const moved = state._movePopulation(from, to, 100_000, false);
    this.assertApprox(moved, 100_000, 1);
    this.assertApprox(state.regionPopulation(from), fromBefore - moved, 1e-6);
    this.assertApprox(state.regionPopulation(to), toBefore + moved, 1e-6);
  }

  test_people_move_toward_the_richer_region() {
    const state = smallState();
    const cities = state.cities.filter((city) => city.civ === 0);
    const rich = cities[0];
    const poor = cities[1];
    // Dense on one side, sparse on the other: with land-based food that makes
    // the sparse region the rich one.
    for (const coords of state.regionTiles(rich)) {
      state.tilePopulation.set(key(coords.x, coords.y), 1_000);
    }
    for (const coords of state.regionTiles(poor)) {
      state.tilePopulation.set(key(coords.x, coords.y), 5_000_000);
    }
    state._gdpPerCapitaCache.clear();
    const richBefore = state.regionPopulation(rich);
    const poorBefore = state.regionPopulation(poor);
    state._migrateForIncome();
    this.assertGreater(state.regionPopulation(rich), richBefore, "people moved to the rich region");
    this.assertLess(state.regionPopulation(poor), poorBefore, "and left the poor one");
  }

  test_a_region_only_moves_to_a_much_richer_one() {
    const state = smallState();
    // Migration levelled the regions at generation, so no one is twice as rich
    // as anyone else and nobody moves.
    const before = state.cities.map((city) => state.regionPopulation(city));
    state._migrateForIncome();
    const after = state.cities.map((city) => state.regionPopulation(city));
    for (let i = 0; i < before.length; i++) {
      this.assertApprox(after[i], before[i], 1e-6, "nobody moved to a merely equal region");
    }
  }

  test_an_airport_caps_its_daily_intake() {
    const state = smallState();
    const cities = state.cities;
    const from = cityOf(state, 0);
    const to = cities.find((city) => city.civ === 1);
    // Every region is dense and equally poor except `to`, which is sparse and
    // so far richer. Only `to` is worth moving to.
    for (const city of cities) {
      const people = city.id === to.id ? 1_000 : 5_000_000;
      for (const coords of state.regionTiles(city)) {
        state.tilePopulation.set(key(coords.x, coords.y), people);
      }
    }
    state._gdpPerCapitaCache.clear();
    const airport = state.protoBuildings.findIndex((b) => b.id === "airport");
    from.buildings[airport] = 1;
    to.buildings[airport] = 1;
    const fromBefore = state.regionPopulation(from);
    state._migrateForIncome();
    const lost = fromBefore - state.regionPopulation(from);
    this.assertGreater(lost, 0, "people flew to the rich region");
    // 1000 people per airport level a day, and the route's level is 1.
    this.assertTrue(lost <= 1_001, `the flight carried at most its capacity, lost ${lost}`);
  }

  test_the_migration_graph_tallies_city_to_city_flows() {
    const state = smallState();
    const from = cityOf(state, 0);
    const to = state.cities.find((city) => city.id !== from.id);
    this.assertNotNull(from, "the fixture has an origin");
    this.assertNotNull(to, "and a destination");
    const moved = state._movePopulation(from, to, 100_000, true);
    this.assertGreater(moved, 0, "people moved");
    const graph = state.snapshot(0).migrationGraph;
    this.assertHas(graph, "links");
    const link = graph.links.find(
      (entry) =>
        entry[0] === from.coords.x && entry[1] === from.coords.y &&
        entry[2] === to.coords.x && entry[3] === to.coords.y
    );
    this.assertNotNull(link, "the city-to-city flow was tallied");
    this.assertApprox(link[4], moved, 1, "the link carries everyone who moved");
  }

  test_the_migration_graph_rolls_over_a_month() {
    const state = smallState();
    const from = cityOf(state, 0);
    const to = state.cities.find((city) => city.id !== from.id);
    state._movePopulation(from, to, 100_000, true);
    this.assertNotEmpty(state.snapshot(0).migrationGraph.links, "the flow is on the graph");
    // Each day archives the last, so a month's worth of empties eventually
    // pushes the only flow out of the rolling window.
    for (let day = 0; day < 31; day++) state._tickMigration();
    this.assertEmpty(state.snapshot(0).migrationGraph.links, "the month-old flow has fallen off");
  }

  test_internal_equalisation_does_not_pollute_the_migration_graph() {
    // The start-of-game levelling moved people with recording off, so the
    // population map opens with no migration arrows.
    const state = smallState();
    this.assertEmpty(state.snapshot(0).migrationGraph.links, "the opening graph is empty");
  }
}