diff --git a/src/hosting/implicitInit.spec.ts b/src/hosting/implicitInit.spec.ts
new file mode 100644
index 00000000000..dc87565197d
--- /dev/null
+++ b/src/hosting/implicitInit.spec.ts
@@ -0,0 +1,79 @@
+import { expect } from "chai";
+import * as sinon from "sinon";
+import { implicitInit } from "./implicitInit";
+import * as fetchWebSetupModule from "../fetchWebSetup";
+import * as templatesModule from "../templates";
+import { EmulatorRegistry } from "../emulator/registry";
+import { Emulators } from "../emulator/types";
+import * as utils from "../utils";
+
+describe("hosting/implicitInit", () => {
+  let fetchWebSetupStub: sinon.SinonStub;
+  let getCachedWebSetupStub: sinon.SinonStub;
+  let readTemplateStub: sinon.SinonStub;
+  let getInfoStub: sinon.SinonStub;
+  let urlStub: sinon.SinonStub;
+  let logWarningStub: sinon.SinonStub;
+
+  beforeEach(() => {
+    fetchWebSetupStub = sinon.stub(fetchWebSetupModule, "fetchWebSetup");
+    getCachedWebSetupStub = sinon.stub(fetchWebSetupModule, "getCachedWebSetup");
+    readTemplateStub = sinon.stub(templatesModule, "readTemplateSync").returns(
+      "/*--CONFIG--*/\n/*--EMULATORS--*/"
+    );
+    getInfoStub = sinon.stub(EmulatorRegistry, "getInfo");
+    urlStub = sinon.stub(EmulatorRegistry, "url");
+    logWarningStub = sinon.stub(utils, "logLabeledWarning");
+  });
+
+  afterEach(() => {
+    sinon.restore();
+  });
+
+  it("should successfully initialize with direct configuration", async () => {
+    const mockConfig = { appId: "my-app" };
+    fetchWebSetupStub.resolves(mockConfig);
+
+    const res = await implicitInit({});
+
+    expect(res.json).to.include('"appId": "my-app"');
+    expect(res.js).to.include("var firebaseConfig = {\n  \"appId\": \"my-app\"\n}");
+    expect(res.js).to.include("var firebaseEmulators = undefined");
+  });
+
+  it("should fallback to cache if fetch fails with 403", async () => {
+    const err: any = new Error("Auth failed");
+    err.context = { response: { statusCode: 403 } };
+    fetchWebSetupStub.rejects(err);
+    getCachedWebSetupStub.returns({ appId: "cached-app" });
+
+    const res = await implicitInit({});
+
+    expect(logWarningStub).to.have.been.calledWithMatch("hosting", /Authentication error/);
+    expect(res.json).to.include('"appId": "cached-app"');
+  });
+
+  it("should log warning when absolutely no config is available", async () => {
+    fetchWebSetupStub.rejects(new Error("Network off"));
+    getCachedWebSetupStub.returns(undefined);
+
+    const res = await implicitInit({});
+
+    expect(logWarningStub).to.have.been.calledWithMatch(
+      "hosting",
+      /Could not fetch web app configuration/
+    );
+    expect(res.json).to.equal(undefined);
+  });
+
+  it("should populate emulators list when active", async () => {
+    fetchWebSetupStub.resolves({ appId: "app" });
+    getInfoStub.withArgs(Emulators.FIRESTORE).returns({ host: "localhost", port: 8080 });
+    urlStub.withArgs(Emulators.FIRESTORE).returns({ host: "localhost:8080" });
+
+    const res = await implicitInit({});
+
+    expect(res.emulatorsJs).to.include('"host": "localhost"');
+    expect(res.emulatorsJs).to.include('"port": 8080');
+  });
+});