allow alliance extension Fixes #491 (#1314)

## Description:

About 30s before an alliance is about to expire, both players receive a
prompt to extend the alliance. If both players agree the alliance is
extended.

## Please complete the following:

- [x] I have added screenshots for all UI updates
- [x] I process any text displayed to the user through translateText()
and I've added it to the en.json file
- [x] I have added relevant tests to the test directory
- [x] I confirm I have thoroughly tested these changes and take full
responsibility for any bugs introduced
- [x] I understand that submitting code with bugs that could have been
caught through manual testing blocks releases and new features for all
contributors

## Please put your Discord username so you can be contacted if a bug or
regression is found:

evan

tests/AllianceExtensionExecution.test.ts

@@ -0,0 +1,72 @@
+import { AllianceExtensionExecution } from "../src/core/execution/alliance/AllianceExtensionExecution";
+import { AllianceRequestExecution } from "../src/core/execution/alliance/AllianceRequestExecution";
+import { AllianceRequestReplyExecution } from "../src/core/execution/alliance/AllianceRequestReplyExecution";
+import { Game, Player, PlayerType } from "../src/core/game/Game";
+import { playerInfo, setup } from "./util/Setup";
+
+let game: Game;
+let player1: Player;
+let player2: Player;
+
+describe("AllianceExtensionExecution", () => {
+  beforeEach(async () => {
+    game = await setup(
+      "ocean_and_land",
+      {
+        infiniteGold: true,
+        instantBuild: true,
+        infiniteTroops: true,
+      },
+      [
+        playerInfo("player1", PlayerType.Human),
+        playerInfo("player2", PlayerType.Human),
+      ],
+    );
+
+    player1 = game.player("player1");
+    player2 = game.player("player2");
+
+    while (game.inSpawnPhase()) {
+      game.executeNextTick();
+    }
+  });
+
+  test("Successfully extends existing alliance", () => {
+    game.addExecution(new AllianceRequestExecution(player1, player2.id()));
+    game.executeNextTick();
+    game.executeNextTick();
+
+    game.addExecution(
+      new AllianceRequestReplyExecution(player1.id(), player2, true),
+    );
+    game.executeNextTick();
+    game.executeNextTick();
+
+    expect(player1.allianceWith(player2)).toBeTruthy();
+    expect(player2.allianceWith(player1)).toBeTruthy();
+
+    const allianceBefore = player1.allianceWith(player2)!;
+    const expirationBefore =
+      allianceBefore.createdAt() + game.config().allianceDuration();
+
+    game.addExecution(new AllianceExtensionExecution(player1, player2.id()));
+    game.executeNextTick();
+
+    const allianceAfter = player1.allianceWith(player2)!;
+
+    expect(allianceAfter.id()).toBe(allianceBefore.id());
+
+    const expirationAfter =
+      allianceAfter.createdAt() + game.config().allianceDuration();
+
+    expect(expirationAfter).toBeGreaterThanOrEqual(expirationBefore);
+  });
+
+  test("Fails gracefully if no alliance exists", () => {
+    game.addExecution(new AllianceExtensionExecution(player1, player2.id()));
+    game.executeNextTick();
+
+    expect(player1.allianceWith(player2)).toBeFalsy();
+    expect(player2.allianceWith(player1)).toBeFalsy();
+  });
+});