fix: force passed locales into faker constructor

src/faker.ts

@@ -36,7 +36,7 @@ export type UsableLocale = LiteralUnion<KnownLocale>;
 export type UsedLocales = Partial<Record<UsableLocale, LocaleDefinition>>;
 
 export interface FakerOptions {
-  locales?: UsedLocales;
+  locales: UsedLocales;
   locale?: UsableLocale;
   localeFallback?: UsableLocale;
 }
@@ -81,8 +81,20 @@ export class Faker {
   readonly vehicle: Vehicle = new Vehicle(this);
   readonly word: Word = new Word(this);
 
-  constructor(opts: FakerOptions = {}) {
-    this.locales = this.locales || opts.locales || {};
+  constructor(opts: FakerOptions) {
+    if (!opts) {
+      throw new Error(
+        'Options with at least one entry in locales must be provided'
+      );
+    }
+
+    if (Object.keys(opts.locales ?? {}).length === 0) {
+      throw new Error(
+        'At least one entry in locales must be provided in the locales parameter'
+      );
+    }
+
+    this.locales = opts.locales;
     this.locale = this.locale || opts.locale || 'en';
     this.localeFallback = this.localeFallback || opts.localeFallback || 'en';
 

test/faker.spec.ts

@@ -1,11 +1,33 @@
 import { beforeEach, describe, expect, it } from 'vitest';
-import { faker } from '../src';
+import { faker, Faker } from '../src';
 
 describe('faker', () => {
   beforeEach(() => {
     faker.locale = 'en';
   });
 
+  it('should throw error if no options passed', () => {
+    expect(
+      () =>
+        // @ts-expect-error: mission options
+        new Faker()
+    ).toThrow(
+      Error('Options with at least one entry in locales must be provided')
+    );
+  });
+
+  it('should throw error if no locales passed', () => {
+    expect(
+      () =>
+        // @ts-expect-error: missing locales
+        new Faker({})
+    ).toThrow(
+      Error(
+        'At least one entry in locales must be provided in the locales parameter'
+      )
+    );
+  });
+
   // This is only here for coverage
   // The actual test is in mersenne.spec.ts
   describe('seed()', () => {