diff --git a/src/hooks/auto-update-checker/checker.test.ts b/src/hooks/auto-update-checker/checker.test.ts
new file mode 100644
index 0000000..0edcac4
--- /dev/null
+++ b/src/hooks/auto-update-checker/checker.test.ts
@@ -0,0 +1,134 @@
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+
+// ─── Fixtures ─────────────────────────────────────────────────────────────────
+
+const { fsMock } = vi.hoisted(() => ({
+  fsMock: {
+    existsSync: vi.fn(),
+    readFileSync: vi.fn(),
+    writeFileSync: vi.fn(),
+    statSync: vi.fn(),
+  },
+}));
+
+vi.mock("node:fs", () => fsMock);
+
+// ─── Tests ────────────────────────────────────────────────────────────────────
+
+describe("isLocalDevMode / getLocalDevPath", () => {
+  beforeEach(() => {
+    vi.resetAllMocks();
+    fsMock.existsSync.mockReturnValue(false);
+  });
+
+  afterEach(() => {
+    vi.restoreAllMocks();
+  });
+
+  it("returns false when no config files exist", async () => {
+    const { isLocalDevMode } = await import("./checker");
+    expect(isLocalDevMode("/some/project")).toBe(false);
+  });
+
+  it("returns null from getLocalDevPath when no config exists", async () => {
+    const { getLocalDevPath } = await import("./checker");
+    expect(getLocalDevPath("/some/project")).toBeNull();
+  });
+
+  it("returns null when config has no matching file:// plugin entry", async () => {
+    const { getLocalDevPath } = await import("./checker");
+    fsMock.existsSync.mockImplementation((p: string) =>
+      p.endsWith("opencode.json"),
+    );
+    fsMock.readFileSync.mockReturnValue(
+      JSON.stringify({ plugin: ["some-other-plugin@1.0.0"] }),
+    );
+    expect(getLocalDevPath("/project")).toBeNull();
+  });
+
+  it("returns path when config contains a file:// entry for the package", async () => {
+    const { getLocalDevPath } = await import("./checker");
+    fsMock.existsSync.mockImplementation((p: string) =>
+      p.endsWith("opencode.json"),
+    );
+    fsMock.readFileSync.mockReturnValue(
+      JSON.stringify({
+        plugin: ["file:///home/user/opencode-antigravity-auth/dist/plugin.js"],
+      }),
+    );
+    const result = getLocalDevPath("/project");
+    expect(result).toContain("opencode-antigravity-auth");
+  });
+
+  it("handles JSONC config with comments and trailing commas", async () => {
+    const { getLocalDevPath } = await import("./checker");
+    fsMock.existsSync.mockImplementation((p: string) =>
+      p.endsWith("opencode.jsonc"),
+    );
+    fsMock.readFileSync.mockReturnValue(
+      `{
+        // dev plugin
+        "plugin": [
+          "file:///home/user/opencode-antigravity-auth/dist/plugin.js",
+        ]
+      }`,
+    );
+    const result = getLocalDevPath("/project");
+    expect(result).toContain("opencode-antigravity-auth");
+  });
+
+  it("returns null and does not throw when config file is malformed JSON", async () => {
+    const { getLocalDevPath } = await import("./checker");
+    fsMock.existsSync.mockReturnValue(true);
+    fsMock.readFileSync.mockReturnValue("{ not valid json !!!}");
+    expect(() => getLocalDevPath("/project")).not.toThrow();
+    expect(getLocalDevPath("/project")).toBeNull();
+  });
+});
+
+describe("findPluginEntry", () => {
+  beforeEach(() => {
+    vi.resetAllMocks();
+    fsMock.existsSync.mockReturnValue(false);
+  });
+
+  it("returns null when no config files exist", async () => {
+    const { findPluginEntry } = await import("./checker");
+    expect(findPluginEntry("/project")).toBeNull();
+  });
+
+  it("returns entry with isPinned=false for bare package name", async () => {
+    const { findPluginEntry } = await import("./checker");
+    fsMock.existsSync.mockImplementation((p: string) => p.endsWith("opencode.json"));
+    fsMock.readFileSync.mockReturnValue(
+      JSON.stringify({ plugin: ["opencode-antigravity-auth"] }),
+    );
+    const result = findPluginEntry("/project");
+    expect(result).not.toBeNull();
+    expect(result!.isPinned).toBe(false);
+    expect(result!.pinnedVersion).toBeNull();
+  });
+
+  it("returns entry with isPinned=true for versioned package", async () => {
+    const { findPluginEntry } = await import("./checker");
+    fsMock.existsSync.mockImplementation((p: string) => p.endsWith("opencode.json"));
+    fsMock.readFileSync.mockReturnValue(
+      JSON.stringify({ plugin: ["opencode-antigravity-auth@1.5.0"] }),
+    );
+    const result = findPluginEntry("/project");
+    expect(result).not.toBeNull();
+    expect(result!.isPinned).toBe(true);
+    expect(result!.pinnedVersion).toBe("1.5.0");
+  });
+
+  it("returns isPinned=false for @latest entry", async () => {
+    const { findPluginEntry } = await import("./checker");
+    fsMock.existsSync.mockImplementation((p: string) => p.endsWith("opencode.json"));
+    fsMock.readFileSync.mockReturnValue(
+      JSON.stringify({ plugin: ["opencode-antigravity-auth@latest"] }),
+    );
+    const result = findPluginEntry("/project");
+    expect(result!.isPinned).toBe(false);
+    expect(result!.pinnedVersion).toBeNull();
+  });
+});