feat: add initial seed parameter to constructors (#3220)

3 files changed, 129 insertions, 21 deletions

diff --git a/test/faker.spec.ts b/test/faker.spec.ts
index 6d928d63..dba19421 100644
--- a/test/faker.spec.ts
+++ b/test/faker.spec.ts
@@ -1,18 +1,10 @@
 import type { MockInstance } from 'vitest';
 import { describe, expect, it, vi } from 'vitest';
-import { Faker, faker } from '../src';
+import { Faker, faker, generateMersenne32Randomizer } from '../src';
 import { FakerError } from '../src/errors/faker-error';
 import { keys } from '../src/internal/keys';
 
 describe('faker', () => {
-  it('should throw error if no locales passed', () => {
-    expect(() => new Faker({ locale: [] })).toThrow(
-      new FakerError(
-        'The locale option must contain at least one locale definition.'
-      )
-    );
-  });
-
   it('should not log anything on startup', async () => {
     const spies: MockInstance[] = keys(console)
       .filter((key) => typeof console[key] === 'function')
@@ -69,19 +61,70 @@ describe('faker', () => {
     });
   });
 
-  describe('randomizer', () => {
-    it('should be possible to provide a custom Randomizer', () => {
-      const customFaker = new Faker({
-        locale: {},
-        randomizer: {
-          next: () => 0,
-          seed: () => void 0,
-        },
+  describe('constructor()', () => {
+    describe('locale', () => {
+      it('should throw error if no locales passed', () => {
+        expect(() => new Faker({ locale: [] })).toThrow(
+          new FakerError(
+            'The locale option must contain at least one locale definition.'
+          )
+        );
+      });
+    });
+
+    describe('randomizer', () => {
+      it('should be possible to provide a custom Randomizer', () => {
+        const customFaker = new Faker({
+          locale: {},
+          randomizer: {
+            next: () => 0,
+            seed: () => void 0,
+          },
+        });
+
+        expect(customFaker.number.int()).toBe(0);
+        expect(customFaker.number.int()).toBe(0);
+        expect(customFaker.number.int()).toBe(0);
+      });
+    });
+
+    describe('seed', () => {
+      it('should be possible to provide an initial seed', () => {
+        const customFaker = new Faker({
+          locale: {},
+          seed: 12345,
+        });
+
+        expect(customFaker.number.int()).toBe(8373237378417847);
+        expect(customFaker.number.int()).toBe(2849657659447330);
+        expect(customFaker.number.int()).toBe(1656593383470774);
+
+        customFaker.seed(12345);
+
+        expect(customFaker.number.int()).toBe(8373237378417847);
+        expect(customFaker.number.int()).toBe(2849657659447330);
+        expect(customFaker.number.int()).toBe(1656593383470774);
       });
+    });
 
-      expect(customFaker.number.int()).toBe(0);
-      expect(customFaker.number.int()).toBe(0);
-      expect(customFaker.number.int()).toBe(0);
+    describe('randomizer+seed', () => {
+      it('should take apply both the randomizer and seed', () => {
+        const customFaker = new Faker({
+          locale: {},
+          randomizer: generateMersenne32Randomizer(67890),
+          seed: 12345,
+        });
+
+        expect(customFaker.number.int()).toBe(8373237322874880);
+        expect(customFaker.number.int()).toBe(8017800868134912);
+        expect(customFaker.number.int()).toBe(2849657711493120);
+
+        customFaker.seed(12345); // Retry with the expected seed
+
+        expect(customFaker.number.int()).toBe(8373237322874880);
+        expect(customFaker.number.int()).toBe(8017800868134912);
+        expect(customFaker.number.int()).toBe(2849657711493120);
+      });
     });
   });
 
diff --git a/test/internal/seed.spec.ts b/test/internal/seed.spec.ts
new file mode 100644
index 00000000..c3503524
--- /dev/null
+++ b/test/internal/seed.spec.ts
@@ -0,0 +1,11 @@
+import { describe, expect, it } from 'vitest';
+import { randomSeed } from '../../src/internal/seed';
+
+describe('seed', () => {
+  it('should generate a random seed', () => {
+    const actual = randomSeed();
+
+    expect(actual).toBeTypeOf('number');
+    expect(actual).not.toBe(randomSeed());
+  });
+});
diff --git a/test/simple-faker.spec.ts b/test/simple-faker.spec.ts
index aa6f00c1..02c860a5 100644
--- a/test/simple-faker.spec.ts
+++ b/test/simple-faker.spec.ts
@@ -1,6 +1,6 @@
 import type { MockInstance } from 'vitest';
 import { describe, expect, it, vi } from 'vitest';
-import { SimpleFaker, simpleFaker } from '../src';
+import { generateMersenne32Randomizer, SimpleFaker, simpleFaker } from '../src';
 import { keys } from '../src/internal/keys';
 
 describe('simpleFaker', () => {
@@ -20,6 +20,60 @@ describe('simpleFaker', () => {
     }
   });
 
+  describe('constructor()', () => {
+    describe('randomizer', () => {
+      it('should be possible to provide a custom Randomizer', () => {
+        const customFaker = new SimpleFaker({
+          randomizer: {
+            next: () => 0,
+            seed: () => void 0,
+          },
+        });
+
+        expect(customFaker.number.int()).toBe(0);
+        expect(customFaker.number.int()).toBe(0);
+        expect(customFaker.number.int()).toBe(0);
+      });
+    });
+
+    describe('seed', () => {
+      it('should be possible to provide an initial seed', () => {
+        const customFaker = new SimpleFaker({
+          seed: 12345,
+        });
+
+        expect(customFaker.number.int()).toBe(8373237378417847);
+        expect(customFaker.number.int()).toBe(2849657659447330);
+        expect(customFaker.number.int()).toBe(1656593383470774);
+
+        customFaker.seed(12345); // Retry with the expected seed
+
+        expect(customFaker.number.int()).toBe(8373237378417847);
+        expect(customFaker.number.int()).toBe(2849657659447330);
+        expect(customFaker.number.int()).toBe(1656593383470774);
+      });
+    });
+
+    describe('randomizer+seed', () => {
+      it('should take apply both the randomizer and seed', () => {
+        const customFaker = new SimpleFaker({
+          randomizer: generateMersenne32Randomizer(67890),
+          seed: 12345,
+        });
+
+        expect(customFaker.number.int()).toBe(8373237322874880);
+        expect(customFaker.number.int()).toBe(8017800868134912);
+        expect(customFaker.number.int()).toBe(2849657711493120);
+
+        customFaker.seed(12345); // Retry with the expected seed
+
+        expect(customFaker.number.int()).toBe(8373237322874880);
+        expect(customFaker.number.int()).toBe(8017800868134912);
+        expect(customFaker.number.int()).toBe(2849657711493120);
+      });
+    });
+  });
+
   // This is only here for coverage
   // The actual test is in mersenne.spec.ts
   describe('seed()', () => {