test: dedupe fixtures and test harness setup

src/gateway/gateway-connection.test-mocks.ts

@@ -0,0 +1,27 @@
+import { vi } from "vitest";
+
+export const loadConfigMock = vi.fn();
+export const resolveGatewayPortMock = vi.fn();
+export const pickPrimaryTailnetIPv4Mock = vi.fn();
+export const pickPrimaryLanIPv4Mock = vi.fn();
+
+vi.mock("../config/config.js", async (importOriginal) => {
+  const actual = await importOriginal<typeof import("../config/config.js")>();
+  return {
+    ...actual,
+    loadConfig: loadConfigMock,
+    resolveGatewayPort: resolveGatewayPortMock,
+  };
+});
+
+vi.mock("../infra/tailnet.js", () => ({
+  pickPrimaryTailnetIPv4: pickPrimaryTailnetIPv4Mock,
+}));
+
+vi.mock("./net.js", async (importOriginal) => {
+  const actual = await importOriginal<typeof import("./net.js")>();
+  return {
+    ...actual,
+    pickPrimaryLanIPv4: pickPrimaryLanIPv4Mock,
+  };
+});