test: add comprehensive automated test coverage

- Vitest multi-project setup (unit / integration / component)
- Real-Postgres integration harness via in-process PGlite (TEST_DATABASE_URL
  override), migrations applied per worker; production code untouched
- Unit: routing, locale, validation/Zod schemas, metadata, mail, site-theme,
  marquee, media, portfolio helpers, plus architecture-rule tests
- Integration: Prisma data layer, API routes, and all server actions
- Component: UI primitives and form components (jsdom + Testing Library)
- 371 tests passing

tests/integration/actions-smtp.test.ts

@@ -0,0 +1,91 @@
+import { beforeEach, describe, expect, it, vi } from "vitest";
+
+vi.mock("next/cache", async () => ({ revalidatePath: (await import("@/tests/helpers/next-mocks")).revalidatePath }));
+vi.mock("next/navigation", async () => ({ redirect: (await import("@/tests/helpers/next-mocks")).redirect }));
+vi.mock("next/dist/client/components/redirect-error", async () => ({
+  isRedirectError: (await import("@/tests/helpers/next-mocks")).isRedirectError,
+}));
+vi.mock("@/lib/admin-auth", async () => {
+  const m = await import("@/tests/helpers/next-mocks");
+  return { isAdminAuthenticated: m.isAdminAuthenticated, clearAdminSessionCookie: m.clearAdminSessionCookie };
+});
+
+const { sendTestEmail } = vi.hoisted(() => ({ sendTestEmail: vi.fn(async () => {}) }));
+vi.mock("@/lib/mail", () => ({ sendTestEmail }));
+
+import { saveMailSettingsAction, sendTestEmailAction } from "@/app/_admin/smtp/actions";
+import { getMailSettings } from "@/lib/app-config";
+import { adminAuth, captureRedirect, formDataFrom, resetNextMocks } from "@/tests/helpers/next-mocks";
+
+beforeEach(() => {
+  resetNextMocks();
+  sendTestEmail.mockClear();
+});
+
+const validForm = {
+  smtpHost: "smtp.example.com",
+  smtpPort: "465",
+  smtpUsername: "mailer",
+  smtpPassword: "secret",
+  smtpSecure: "on",
+  mailFromEmail: "from@example.com",
+  mailFromName: "Studio",
+  mailContactRecipient: "contact@example.com",
+  mailTestRecipient: "test@example.com",
+};
+
+describe("saveMailSettingsAction", () => {
+  it("persists valid settings and redirects with success", async () => {
+    const url = await captureRedirect(() => saveMailSettingsAction(formDataFrom(validForm)));
+    expect(url).toContain("success=");
+
+    const settings = await getMailSettings();
+    expect(settings.smtp.host).toBe("smtp.example.com");
+    expect(settings.smtp.port).toBe(465);
+    expect(settings.smtp.secure).toBe(true);
+    expect(settings.recipients.contact).toBe("contact@example.com");
+  });
+
+  it("rejects an invalid port with an error flash", async () => {
+    const url = await captureRedirect(() =>
+      saveMailSettingsAction(formDataFrom({ ...validForm, smtpPort: "not-a-number" })),
+    );
+    expect(url).toContain("error=");
+  });
+
+  it("retains the existing password when the field is left blank", async () => {
+    await captureRedirect(() => saveMailSettingsAction(formDataFrom(validForm)));
+    await captureRedirect(() =>
+      saveMailSettingsAction(formDataFrom({ ...validForm, smtpPassword: "" })),
+    );
+    const settings = await getMailSettings();
+    expect(settings.smtp.password).toBe("secret");
+  });
+
+  it("redirects unauthenticated callers to the admin root", async () => {
+    adminAuth.authenticated = false;
+    const url = await captureRedirect(() => saveMailSettingsAction(formDataFrom(validForm)));
+    expect(url).toBe("/");
+  });
+});
+
+describe("sendTestEmailAction", () => {
+  it("sends a test email and redirects with success", async () => {
+    const url = await captureRedirect(() => sendTestEmailAction());
+    expect(sendTestEmail).toHaveBeenCalledTimes(1);
+    expect(url).toContain("success=");
+  });
+
+  it("redirects with an error when sending fails", async () => {
+    sendTestEmail.mockRejectedValueOnce(new Error("SMTP host is required."));
+    const url = await captureRedirect(() => sendTestEmailAction());
+    expect(url).toContain("error=");
+  });
+
+  it("redirects unauthenticated callers to the admin root", async () => {
+    adminAuth.authenticated = false;
+    const url = await captureRedirect(() => sendTestEmailAction());
+    expect(url).toBe("/");
+    expect(sendTestEmail).not.toHaveBeenCalled();
+  });
+});