diff --git a/packages/auth/src/__factories__/index.ts b/packages/auth/src/__factories__/index.ts
new file mode 100644
index 0000000..abe677e
--- /dev/null
+++ b/packages/auth/src/__factories__/index.ts
@@ -0,0 +1,2 @@
+export { userFactory } from "./user.factory.js";
+export { sessionFactory } from "./session.factory.js";
diff --git a/packages/auth/src/__factories__/session.factory.test.ts b/packages/auth/src/__factories__/session.factory.test.ts
new file mode 100644
index 0000000..1d1df35
--- /dev/null
+++ b/packages/auth/src/__factories__/session.factory.test.ts
@@ -0,0 +1,26 @@
+import { describe, it, expect, beforeEach } from "vitest";
+import { sessionFactory } from "@/__factories__/session.factory";
+
+describe("sessionFactory", () => {
+  beforeEach(() => sessionFactory.reset());
+
+  it("returns a Session with stable defaults", () => {
+    const s = sessionFactory.build();
+    expect(s.id).toBe("session-1");
+    expect(s.userId).toBe("user-1");
+    expect(s.expiresAt).toBeInstanceOf(Date);
+  });
+
+  it("applies overrides", () => {
+    const s = sessionFactory.build({ userId: "user-42" });
+    expect(s.userId).toBe("user-42");
+    expect(s.id).toBe("session-1");
+  });
+
+  it("increments sequence per build", () => {
+    const a = sessionFactory.build();
+    const b = sessionFactory.build();
+    expect(a.id).toBe("session-1");
+    expect(b.id).toBe("session-2");
+  });
+});
diff --git a/packages/auth/src/__factories__/session.factory.ts b/packages/auth/src/__factories__/session.factory.ts
new file mode 100644
index 0000000..c9a7a32
--- /dev/null
+++ b/packages/auth/src/__factories__/session.factory.ts
@@ -0,0 +1,8 @@
+import { defineFactory } from "@repo/core-testing/factory";
+import type { Session } from "../entities/session.js";
+
+export const sessionFactory = defineFactory<Session>(({ sequence }) => ({
+  id: `session-${sequence}`,
+  userId: "user-1",
+  expiresAt: new Date("2026-12-31T23:59:59Z"),
+}));
diff --git a/packages/auth/src/__factories__/user.factory.test.ts b/packages/auth/src/__factories__/user.factory.test.ts
new file mode 100644
index 0000000..054c00a
--- /dev/null
+++ b/packages/auth/src/__factories__/user.factory.test.ts
@@ -0,0 +1,26 @@
+import { describe, it, expect, beforeEach } from "vitest";
+import { userFactory } from "@/__factories__/user.factory";
+
+describe("userFactory", () => {
+  beforeEach(() => userFactory.reset());
+
+  it("returns a User with stable defaults", () => {
+    const u = userFactory.build();
+    expect(u.id).toBe("user-1");
+    expect(u.username).toBe("user1");
+    expect(u.passwordHash).toHaveLength(60);
+  });
+
+  it("applies overrides", () => {
+    const u = userFactory.build({ username: "alice" });
+    expect(u.username).toBe("alice");
+    expect(u.id).toBe("user-1");
+  });
+
+  it("increments sequence per build", () => {
+    const a = userFactory.build();
+    const b = userFactory.build();
+    expect(a.id).toBe("user-1");
+    expect(b.id).toBe("user-2");
+  });
+});
diff --git a/packages/auth/src/__factories__/user.factory.ts b/packages/auth/src/__factories__/user.factory.ts
new file mode 100644
index 0000000..edf06e5
--- /dev/null
+++ b/packages/auth/src/__factories__/user.factory.ts
@@ -0,0 +1,8 @@
+import { defineFactory } from "@repo/core-testing/factory";
+import type { User } from "../entities/user.js";
+
+export const userFactory = defineFactory<User>(({ sequence }) => ({
+  id: `user-${sequence}`,
+  username: `user${sequence}`,
+  passwordHash: `$2b$10$stablehashfortest${sequence}`.padEnd(60, "x"),
+}));
diff --git a/packages/blog/src/__factories__/article.factory.test.ts b/packages/blog/src/__factories__/article.factory.test.ts
new file mode 100644
index 0000000..115a037
--- /dev/null
+++ b/packages/blog/src/__factories__/article.factory.test.ts
@@ -0,0 +1,27 @@
+import { describe, it, expect, beforeEach } from "vitest";
+import { articleFactory } from "@/__factories__/article.factory";
+
+describe("articleFactory", () => {
+  beforeEach(() => articleFactory.reset());
+
+  it("returns an Article with stable defaults", () => {
+    const a = articleFactory.build();
+    expect(a.title).toBe("Article 1");
+    expect(a.slug).toBe("article-1");
+    expect(a.status).toBe("draft");
+    expect(a.createdAt).toEqual(new Date("2026-01-01T00:00:00Z"));
+  });
+
+  it("applies overrides", () => {
+    const a = articleFactory.build({ status: "published", title: "X" });
+    expect(a.status).toBe("published");
+    expect(a.title).toBe("X");
+  });
+
+  it("increments sequence per build", () => {
+    const a = articleFactory.build();
+    const b = articleFactory.build();
+    expect(a.id).toBe("article-1");
+    expect(b.id).toBe("article-2");
+  });
+});
diff --git a/packages/blog/src/__factories__/article.factory.ts b/packages/blog/src/__factories__/article.factory.ts
new file mode 100644
index 0000000..82b87b4
--- /dev/null
+++ b/packages/blog/src/__factories__/article.factory.ts
@@ -0,0 +1,13 @@
+import { defineFactory } from "@repo/core-testing/factory";
+import type { Article } from "../entities/article.js";
+
+export const articleFactory = defineFactory<Article>(({ sequence }) => ({
+  id: `article-${sequence}`,
+  title: `Article ${sequence}`,
+  slug: `article-${sequence}`,
+  content: null,
+  status: "draft",
+  authorId: "user-1",
+  createdAt: new Date("2026-01-01T00:00:00Z"),
+  updatedAt: new Date("2026-01-01T00:00:00Z"),
+}));
diff --git a/packages/blog/src/__factories__/index.ts b/packages/blog/src/__factories__/index.ts
new file mode 100644
index 0000000..2cf271f
--- /dev/null
+++ b/packages/blog/src/__factories__/index.ts
@@ -0,0 +1 @@
+export { articleFactory } from "./article.factory.js";
diff --git a/packages/blog/src/application/use-cases/get-articles.use-case.test.ts b/packages/blog/src/application/use-cases/get-articles.use-case.test.ts
index f88b334..8a83850 100644
--- a/packages/blog/src/application/use-cases/get-articles.use-case.test.ts
+++ b/packages/blog/src/application/use-cases/get-articles.use-case.test.ts
@@ -3,6 +3,7 @@ import { blogContainer } from "../../di/container";
 import { BLOG_SYMBOLS } from "../../di/symbols";
 import type { IArticlesRepository } from "../../application/repositories/articles-repository.interface";
 import { MockArticlesRepository } from "../../infrastructure/repositories/mock-articles.repository";
+import { articleFactory } from "../../__factories__/article.factory";
 import { getArticlesUseCase } from "./get-articles.use-case";
 
 describe("getArticlesUseCase", () => {
@@ -16,47 +17,19 @@ describe("getArticlesUseCase", () => {
     blogContainer
       .bind<IArticlesRepository>(BLOG_SYMBOLS.IArticlesRepository)
       .toConstantValue(repo);
+    articleFactory.reset();
   });
 
   it("returns all articles with no filters", async () => {
-    const now = new Date();
-    await repo.createArticle({
-      id: "1",
-      title: "A",
-      slug: "a",
-      content: null,
-      status: "draft",
-      authorId: "u1",
-      createdAt: now,
-      updatedAt: now,
-    });
+    await repo.createArticle(articleFactory.build({ id: "1", title: "A", slug: "a" }));
     const result = await getArticlesUseCase();
     expect(result).toHaveLength(1);
     expect(result[0]?.id).toBe("1");
   });
 
   it("filters by status", async () => {
-    const now = new Date();
-    await repo.createArticle({
-      id: "1",
-      title: "A",
-      slug: "a",
-      content: null,
-      status: "draft",
-      authorId: "u1",
-      createdAt: now,
-      updatedAt: now,
-    });
-    await repo.createArticle({
-      id: "2",
-      title: "B",
-      slug: "b",
-      content: null,
-      status: "published",
-      authorId: "u1",
-      createdAt: now,
-      updatedAt: now,
-    });
+    await repo.createArticle(articleFactory.build({ id: "1", title: "A", slug: "a", status: "draft" }));
+    await repo.createArticle(articleFactory.build({ id: "2", title: "B", slug: "b", status: "published" }));
     const result = await getArticlesUseCase({ status: "published" });
     expect(result).toHaveLength(1);
     expect(result[0]?.id).toBe("2");
diff --git a/packages/marketing-pages/src/__factories__/index.ts b/packages/marketing-pages/src/__factories__/index.ts
new file mode 100644
index 0000000..b00e38a
--- /dev/null
+++ b/packages/marketing-pages/src/__factories__/index.ts
@@ -0,0 +1,2 @@
+export { pageFactory } from "./page.factory.js";
+export { siteSettingsFactory } from "./site-settings.factory.js";
diff --git a/packages/marketing-pages/src/__factories__/page.factory.test.ts b/packages/marketing-pages/src/__factories__/page.factory.test.ts
new file mode 100644
index 0000000..9896720
--- /dev/null
+++ b/packages/marketing-pages/src/__factories__/page.factory.test.ts
@@ -0,0 +1,29 @@
+import { describe, it, expect, beforeEach } from "vitest";
+import { pageFactory } from "@/__factories__/page.factory";
+
+describe("pageFactory", () => {
+  beforeEach(() => pageFactory.reset());
+
+  it("returns a Page with stable defaults", () => {
+    const p = pageFactory.build();
+    expect(p.id).toBe("page-1");
+    expect(p.title).toBe("Page 1");
+    expect(p.slug).toBe("page-1");
+    expect(p.status).toBe("draft");
+    expect(p.createdAt).toEqual(new Date("2026-01-01T00:00:00Z"));
+  });
+
+  it("applies overrides", () => {
+    const p = pageFactory.build({ status: "published", title: "About" });
+    expect(p.status).toBe("published");
+    expect(p.title).toBe("About");
+    expect(p.id).toBe("page-1");
+  });
+
+  it("increments sequence per build", () => {
+    const a = pageFactory.build();
+    const b = pageFactory.build();
+    expect(a.id).toBe("page-1");
+    expect(b.id).toBe("page-2");
+  });
+});
diff --git a/packages/marketing-pages/src/__factories__/page.factory.ts b/packages/marketing-pages/src/__factories__/page.factory.ts
new file mode 100644
index 0000000..9c616a4
--- /dev/null
+++ b/packages/marketing-pages/src/__factories__/page.factory.ts
@@ -0,0 +1,19 @@
+import { defineFactory } from "@repo/core-testing/factory";
+import type { Page } from "../entities/page.js";
+
+export const pageFactory = defineFactory<Page>(({ sequence }) => ({
+  id: `page-${sequence}`,
+  title: `Page ${sequence}`,
+  slug: `page-${sequence}`,
+  hero: {
+    heading: `Hero ${sequence}`,
+  },
+  layout: [],
+  status: "draft",
+  publishedAt: null,
+  seo: {
+    title: `Page ${sequence} | Site`,
+  },
+  createdAt: new Date("2026-01-01T00:00:00Z"),
+  updatedAt: new Date("2026-01-01T00:00:00Z"),
+}));
diff --git a/packages/marketing-pages/src/__factories__/site-settings.factory.test.ts b/packages/marketing-pages/src/__factories__/site-settings.factory.test.ts
new file mode 100644
index 0000000..3ec33a5
--- /dev/null
+++ b/packages/marketing-pages/src/__factories__/site-settings.factory.test.ts
@@ -0,0 +1,23 @@
+import { describe, it, expect, beforeEach } from "vitest";
+import { siteSettingsFactory } from "@/__factories__/site-settings.factory";
+
+describe("siteSettingsFactory", () => {
+  beforeEach(() => siteSettingsFactory.reset());
+
+  it("returns SiteSettings with stable defaults", () => {
+    const s = siteSettingsFactory.build();
+    expect(s.siteName).toBe("Site 1");
+  });
+
+  it("applies overrides", () => {
+    const s = siteSettingsFactory.build({ siteName: "My Brand" });
+    expect(s.siteName).toBe("My Brand");
+  });
+
+  it("increments sequence per build (siteName reflects it)", () => {
+    const a = siteSettingsFactory.build();
+    const b = siteSettingsFactory.build();
+    expect(a.siteName).toBe("Site 1");
+    expect(b.siteName).toBe("Site 2");
+  });
+});
diff --git a/packages/marketing-pages/src/__factories__/site-settings.factory.ts b/packages/marketing-pages/src/__factories__/site-settings.factory.ts
new file mode 100644
index 0000000..7bdac70
--- /dev/null
+++ b/packages/marketing-pages/src/__factories__/site-settings.factory.ts
@@ -0,0 +1,6 @@
+import { defineFactory } from "@repo/core-testing/factory";
+import type { SiteSettings } from "../entities/site-settings.js";
+
+export const siteSettingsFactory = defineFactory<SiteSettings>(({ sequence }) => ({
+  siteName: `Site ${sequence}`,
+}));
diff --git a/packages/media/package.json b/packages/media/package.json
index 8155269..e7534af 100644
--- a/packages/media/package.json
+++ b/packages/media/package.json
@@ -18,6 +18,7 @@
   },
   "devDependencies": {
     "@repo/core-eslint": "workspace:*",
+    "@repo/core-testing": "workspace:*",
     "@repo/core-typescript": "workspace:*",
     "vitest": "^3.1.0"
   }
diff --git a/packages/media/src/__factories__/index.ts b/packages/media/src/__factories__/index.ts
new file mode 100644
index 0000000..b5dc1be
--- /dev/null
+++ b/packages/media/src/__factories__/index.ts
@@ -0,0 +1 @@
+export { mediaFactory, type Media } from "./media.factory.js";
diff --git a/packages/media/src/__factories__/media.factory.test.ts b/packages/media/src/__factories__/media.factory.test.ts
new file mode 100644
index 0000000..7e6e853
--- /dev/null
+++ b/packages/media/src/__factories__/media.factory.test.ts
@@ -0,0 +1,28 @@
+import { describe, it, expect, beforeEach } from "vitest";
+import { mediaFactory } from "@/__factories__/media.factory";
+
+describe("mediaFactory", () => {
+  beforeEach(() => mediaFactory.reset());
+
+  it("returns a Media object with stable defaults", () => {
+    const m = mediaFactory.build();
+    expect(m.id).toBe("media-1");
+    expect(m.alt).toBe("Media 1");
+    expect(m.mimeType).toBe("image/png");
+    expect(m.filesize).toBe(1024);
+  });
+
+  it("applies overrides", () => {
+    const m = mediaFactory.build({ alt: "Custom alt", mimeType: "image/jpeg" });
+    expect(m.alt).toBe("Custom alt");
+    expect(m.mimeType).toBe("image/jpeg");
+    expect(m.id).toBe("media-1");
+  });
+
+  it("increments sequence per build", () => {
+    const a = mediaFactory.build();
+    const b = mediaFactory.build();
+    expect(a.id).toBe("media-1");
+    expect(b.id).toBe("media-2");
+  });
+});
diff --git a/packages/media/src/__factories__/media.factory.ts b/packages/media/src/__factories__/media.factory.ts
new file mode 100644
index 0000000..2ddb43f
--- /dev/null
+++ b/packages/media/src/__factories__/media.factory.ts
@@ -0,0 +1,19 @@
+import { defineFactory } from "@repo/core-testing/factory";
+
+export interface Media {
+  id: string;
+  alt: string;
+  url: string;
+  filename: string;
+  mimeType: string;
+  filesize: number;
+}
+
+export const mediaFactory = defineFactory<Media>(({ sequence }) => ({
+  id: `media-${sequence}`,
+  alt: `Media ${sequence}`,
+  url: `https://cdn.example.com/media-${sequence}.png`,
+  filename: `media-${sequence}.png`,
+  mimeType: "image/png",
+  filesize: 1024,
+}));
diff --git a/packages/media/tsconfig.json b/packages/media/tsconfig.json
index 7b40882..e6c2727 100644
--- a/packages/media/tsconfig.json
+++ b/packages/media/tsconfig.json
@@ -2,7 +2,11 @@
   "extends": "@repo/core-typescript/base.json",
   "compilerOptions": {
     "outDir": "dist",
-    "lib": ["ES2022", "DOM"]
+    "rootDir": ".",
+    "lib": ["ES2022", "DOM"],
+    "paths": {
+      "@/*": ["./src/*"]
+    }
   },
   "include": ["src/**/*"],
   "exclude": ["node_modules", "dist"]
diff --git a/packages/media/vitest.config.ts b/packages/media/vitest.config.ts
new file mode 100644
index 0000000..2ee07c1
--- /dev/null
+++ b/packages/media/vitest.config.ts
@@ -0,0 +1,9 @@
+import path from "node:path";
+import { mergeConfig } from "vitest/config";
+import { nodeVitestConfig } from "@repo/core-typescript/vitest.base.node";
+
+export default mergeConfig(nodeVitestConfig, {
+  resolve: {
+    alias: { "@": path.resolve(__dirname, "./src") },
+  },
+});
diff --git a/packages/navigation/src/__factories__/header.factory.test.ts b/packages/navigation/src/__factories__/header.factory.test.ts
new file mode 100644
index 0000000..6f8222b
--- /dev/null
+++ b/packages/navigation/src/__factories__/header.factory.test.ts
@@ -0,0 +1,29 @@
+import { describe, it, expect, beforeEach } from "vitest";
+import { headerFactory } from "@/__factories__/header.factory";
+
+describe("headerFactory", () => {
+  beforeEach(() => headerFactory.reset());
+
+  it("returns a Header with stable defaults", () => {
+    const h = headerFactory.build();
+    expect(h.items).toHaveLength(0);
+    expect(h.logoId).toBeUndefined();
+  });
+
+  it("applies overrides", () => {
+    const h = headerFactory.build({
+      logoId: "logo-42",
+      items: [{ label: "Home", href: "/", external: false }],
+    });
+    expect(h.logoId).toBe("logo-42");
+    expect(h.items).toHaveLength(1);
+    expect(h.items[0]?.label).toBe("Home");
+  });
+
+  it("builds multiple headers independently", () => {
+    const a = headerFactory.build({ items: [{ label: "A", href: "/a", external: false }] });
+    const b = headerFactory.build({ items: [] });
+    expect(a.items).toHaveLength(1);
+    expect(b.items).toHaveLength(0);
+  });
+});
diff --git a/packages/navigation/src/__factories__/header.factory.ts b/packages/navigation/src/__factories__/header.factory.ts
new file mode 100644
index 0000000..225b1b8
--- /dev/null
+++ b/packages/navigation/src/__factories__/header.factory.ts
@@ -0,0 +1,6 @@
+import { defineFactory } from "@repo/core-testing/factory";
+import type { Header } from "../entities/header.js";
+
+export const headerFactory = defineFactory<Header>(() => ({
+  items: [],
+}));
diff --git a/packages/navigation/src/__factories__/index.ts b/packages/navigation/src/__factories__/index.ts
new file mode 100644
index 0000000..bd3d794
--- /dev/null
+++ b/packages/navigation/src/__factories__/index.ts
@@ -0,0 +1 @@
+export { headerFactory } from "./header.factory.js";
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index 24f3e5d..20049ea 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -601,6 +601,9 @@ importers:
       '@repo/core-eslint':
         specifier: workspace:*
         version: link:../core-eslint
+      '@repo/core-testing':
+        specifier: workspace:*
+        version: link:../core-testing
       '@repo/core-typescript':
         specifier: workspace:*
         version: link:../core-typescript