Implement the 004-edit-combatant feature that adds the possibility to change a combatants name

packages/domain/src/__tests__/edit-combatant.test.ts

@@ -0,0 +1,163 @@
+import { describe, expect, it } from "vitest";
+import { editCombatant } from "../edit-combatant.js";
+import type { Combatant, Encounter } from "../types.js";
+import { combatantId, isDomainError } from "../types.js";
+
+// --- Helpers ---
+
+function makeCombatant(name: string): Combatant {
+	return { id: combatantId(name), name };
+}
+
+const Alice = makeCombatant("Alice");
+const Bob = makeCombatant("Bob");
+
+function enc(
+	combatants: Combatant[],
+	activeIndex = 0,
+	roundNumber = 1,
+): Encounter {
+	return { combatants, activeIndex, roundNumber };
+}
+
+function successResult(encounter: Encounter, id: string, newName: string) {
+	const result = editCombatant(encounter, combatantId(id), newName);
+	if (isDomainError(result)) {
+		throw new Error(`Expected success, got error: ${result.message}`);
+	}
+	return result;
+}
+
+// --- Acceptance Scenarios (T004) ---
+
+describe("editCombatant", () => {
+	describe("acceptance scenarios", () => {
+		it("scenario 1: rename succeeds with correct event containing combatantId, oldName, newName", () => {
+			const e = enc([Alice, Bob]);
+			const { encounter, events } = successResult(e, "Bob", "Robert");
+
+			expect(encounter.combatants[1]).toEqual({
+				id: combatantId("Bob"),
+				name: "Robert",
+			});
+			expect(events).toEqual([
+				{
+					type: "CombatantUpdated",
+					combatantId: combatantId("Bob"),
+					oldName: "Bob",
+					newName: "Robert",
+				},
+			]);
+		});
+
+		it("scenario 2: activeIndex and roundNumber preserved when renaming the active combatant", () => {
+			const e = enc([Alice, Bob], 1, 3);
+			const { encounter } = successResult(e, "Bob", "Robert");
+
+			expect(encounter.activeIndex).toBe(1);
+			expect(encounter.roundNumber).toBe(3);
+			expect(encounter.combatants[1].name).toBe("Robert");
+		});
+
+		it("scenario 3: combatant list order preserved", () => {
+			const Cael = makeCombatant("Cael");
+			const e = enc([Alice, Bob, Cael]);
+			const { encounter } = successResult(e, "Bob", "Robert");
+
+			expect(encounter.combatants.map((c) => c.name)).toEqual([
+				"Alice",
+				"Robert",
+				"Cael",
+			]);
+		});
+
+		it("scenario 4: renaming to same name still emits event", () => {
+			const e = enc([Alice, Bob]);
+			const { encounter, events } = successResult(e, "Bob", "Bob");
+
+			expect(encounter.combatants[1].name).toBe("Bob");
+			expect(events).toHaveLength(1);
+			expect(events[0]).toEqual({
+				type: "CombatantUpdated",
+				combatantId: combatantId("Bob"),
+				oldName: "Bob",
+				newName: "Bob",
+			});
+		});
+	});
+
+	// --- Invariant Tests (T005) ---
+
+	describe("invariants", () => {
+		it("INV-1: determinism — same inputs produce same outputs", () => {
+			const e = enc([Alice, Bob], 1, 3);
+			const result1 = editCombatant(e, combatantId("Alice"), "Aria");
+			const result2 = editCombatant(e, combatantId("Alice"), "Aria");
+			expect(result1).toEqual(result2);
+		});
+
+		it("INV-2: exactly one event emitted on success", () => {
+			const e = enc([Alice, Bob]);
+			const { events } = successResult(e, "Alice", "Aria");
+			expect(events).toHaveLength(1);
+			expect(events[0].type).toBe("CombatantUpdated");
+		});
+
+		it("INV-3: original encounter is not mutated", () => {
+			const e = enc([Alice, Bob], 0, 1);
+			const originalCombatants = [...e.combatants];
+			const originalActiveIndex = e.activeIndex;
+			const originalRoundNumber = e.roundNumber;
+
+			successResult(e, "Alice", "Aria");
+
+			expect(e.combatants).toEqual(originalCombatants);
+			expect(e.activeIndex).toBe(originalActiveIndex);
+			expect(e.roundNumber).toBe(originalRoundNumber);
+		});
+	});
+
+	// --- Error Scenarios (T011) ---
+
+	describe("error scenarios", () => {
+		it("non-existent id returns combatant-not-found error", () => {
+			const e = enc([Alice, Bob]);
+			const result = editCombatant(e, combatantId("nonexistent"), "NewName");
+
+			expect(isDomainError(result)).toBe(true);
+			if (isDomainError(result)) {
+				expect(result.code).toBe("combatant-not-found");
+			}
+		});
+
+		it("empty name returns invalid-name error", () => {
+			const e = enc([Alice, Bob]);
+			const result = editCombatant(e, combatantId("Alice"), "");
+
+			expect(isDomainError(result)).toBe(true);
+			if (isDomainError(result)) {
+				expect(result.code).toBe("invalid-name");
+			}
+		});
+
+		it("whitespace-only name returns invalid-name error", () => {
+			const e = enc([Alice, Bob]);
+			const result = editCombatant(e, combatantId("Alice"), "   ");
+
+			expect(isDomainError(result)).toBe(true);
+			if (isDomainError(result)) {
+				expect(result.code).toBe("invalid-name");
+			}
+		});
+
+		it("empty encounter returns combatant-not-found for any id", () => {
+			const e = enc([]);
+			const result = editCombatant(e, combatantId("any"), "Name");
+
+			expect(isDomainError(result)).toBe(true);
+			if (isDomainError(result)) {
+				expect(result.code).toBe("combatant-not-found");
+			}
+		});
+	});
+});