diff --git a/desktop/flipper-server-core/src/plugins/PluginManager.tsx b/desktop/flipper-server-core/src/plugins/PluginManager.tsx
index 5c71fe6ce..2f38a0631 100644
--- a/desktop/flipper-server-core/src/plugins/PluginManager.tsx
+++ b/desktop/flipper-server-core/src/plugins/PluginManager.tsx
@@ -50,7 +50,7 @@ const isExecuteMessage = (message: object): message is ExecuteMessage =>
   (message as ExecuteMessage).method === 'execute';
 
 export class PluginManager {
-  private readonly serverAddOns = new Map<string, ServerAddOnManager>();
+  public readonly serverAddOns = new Map<string, ServerAddOnManager>();
 
   constructor(private readonly flipperServer: FlipperServerForServerAddOn) {}
 
diff --git a/desktop/flipper-server-core/src/plugins/__tests__/PluginManager.node.tsx b/desktop/flipper-server-core/src/plugins/__tests__/PluginManager.node.tsx
new file mode 100644
index 000000000..fb8b9d11d
--- /dev/null
+++ b/desktop/flipper-server-core/src/plugins/__tests__/PluginManager.node.tsx
@@ -0,0 +1,214 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @format
+ */
+
+import {ServerAddOnStartDetails} from 'flipper-common';
+import {loadServerAddOn} from '../loadServerAddOn';
+import {PluginManager} from '../PluginManager';
+import {ServerAddOnManager} from '../ServerAddManager';
+import {ServerAddOnModuleToDesktopConnection} from '../ServerAddOnModuleToDesktopConnection';
+import {
+  createControlledPromise,
+  detailsBundled,
+  detailsInstalled,
+  initialOwner,
+  pluginName,
+} from './utils';
+
+jest.mock('../loadServerAddOn');
+const loadServerAddOnMock = loadServerAddOn as jest.Mock;
+
+describe('PluginManager', () => {
+  describe('server add-ons', () => {
+    const startServerAddOn = async (details: ServerAddOnStartDetails) => {
+      const addOnCleanupMock = jest.fn();
+      const addOnMock = jest.fn().mockImplementation(() => addOnCleanupMock);
+      loadServerAddOnMock.mockImplementation(() => ({
+        default: addOnMock,
+      }));
+
+      const flipperServer = {
+        connect: jest.fn(),
+        on: jest.fn(),
+        off: jest.fn(),
+        exec: jest.fn(),
+        close: jest.fn(),
+        emit: jest.fn(),
+      };
+
+      expect(loadServerAddOnMock).toBeCalledTimes(0);
+      expect(addOnMock).toBeCalledTimes(0);
+      expect(addOnCleanupMock).toBeCalledTimes(0);
+
+      const pluginManager = new PluginManager(flipperServer);
+      await pluginManager.startServerAddOn(pluginName, details, initialOwner);
+
+      expect(loadServerAddOnMock).toBeCalledTimes(1);
+      expect(loadServerAddOnMock).toBeCalledWith(pluginName, details);
+      expect(addOnMock).toBeCalledTimes(1);
+      expect(addOnMock).toBeCalledWith(
+        expect.any(ServerAddOnModuleToDesktopConnection),
+        {
+          flipperServer,
+        },
+      );
+      expect(pluginManager.serverAddOns.size).toBe(1);
+
+      const serverAddOn = pluginManager.serverAddOns.get(pluginName);
+      expect(serverAddOn).toBeInstanceOf(ServerAddOnManager);
+      expect(serverAddOn!.state.is('active')).toBeTruthy();
+
+      return {
+        addOnCleanupMock,
+        addOnMock,
+        flipperServer,
+        pluginManager,
+      };
+    };
+
+    describe.each([
+      ['bundled', detailsBundled],
+      ['installed', detailsInstalled],
+    ])('%s', (_name, details) => {
+      test('stops the add-on when the initial owner is removed', async () => {
+        const {pluginManager, addOnCleanupMock} = await startServerAddOn(
+          details,
+        );
+
+        const controlledP = createControlledPromise<void>();
+        addOnCleanupMock.mockImplementation(() => controlledP.promise);
+
+        const stopPromise = pluginManager.stopServerAddOn(
+          pluginName,
+          initialOwner,
+        );
+
+        expect(pluginManager.serverAddOns.size).toBe(1);
+
+        controlledP.resolve();
+        await stopPromise;
+
+        expect(addOnCleanupMock).toBeCalledTimes(1);
+        expect(pluginManager.serverAddOns.size).toBe(0);
+      });
+
+      test('adds a new owner, stops the add-on when all owners are removed', async () => {
+        const {pluginManager, addOnCleanupMock} = await startServerAddOn(
+          details,
+        );
+
+        const newOwner = 'luke';
+        await pluginManager.startServerAddOn(pluginName, details, newOwner);
+        expect(pluginManager.serverAddOns.size).toBe(1);
+
+        await pluginManager.stopServerAddOn(pluginName, initialOwner);
+        expect(addOnCleanupMock).toBeCalledTimes(0);
+        expect(pluginManager.serverAddOns.size).toBe(1);
+
+        const serverAddOn = pluginManager.serverAddOns.get(pluginName)!;
+        expect(serverAddOn.state.is('active')).toBeTruthy();
+
+        await pluginManager.stopServerAddOn(pluginName, newOwner);
+        expect(addOnCleanupMock).toBeCalledTimes(1);
+        expect(pluginManager.serverAddOns.size).toBe(0);
+
+        await serverAddOn.state.wait('inactive');
+      });
+
+      test('concurrent calls to startServerAddOn start a single add-on', async () => {
+        const addOnCleanupMock = jest.fn();
+        const controlledP = createControlledPromise<() => void>();
+        const addOnMock = jest
+          .fn()
+          .mockImplementation(() => controlledP.promise);
+        loadServerAddOnMock.mockImplementation(() => ({
+          default: addOnMock,
+        }));
+
+        const flipperServer = {
+          connect: jest.fn(),
+          on: jest.fn(),
+          off: jest.fn(),
+          exec: jest.fn(),
+          close: jest.fn(),
+          emit: jest.fn(),
+        };
+
+        expect(loadServerAddOnMock).toBeCalledTimes(0);
+        expect(addOnMock).toBeCalledTimes(0);
+        expect(addOnCleanupMock).toBeCalledTimes(0);
+
+        const pluginManager = new PluginManager(flipperServer);
+
+        const startP1 = pluginManager.startServerAddOn(
+          pluginName,
+          details,
+          initialOwner,
+        );
+
+        expect(loadServerAddOnMock).toBeCalledTimes(1);
+        expect(loadServerAddOnMock).toBeCalledWith(pluginName, details);
+        expect(addOnMock).toBeCalledTimes(1);
+        expect(addOnMock).toBeCalledWith(
+          expect.any(ServerAddOnModuleToDesktopConnection),
+          {
+            flipperServer,
+          },
+        );
+
+        expect(pluginManager.serverAddOns.size).toBe(1);
+
+        const newOwner = 'luke';
+        const startP2 = pluginManager.startServerAddOn(
+          pluginName,
+          details,
+          newOwner,
+        );
+
+        expect(loadServerAddOnMock).toBeCalledTimes(1);
+        expect(addOnMock).toBeCalledTimes(1);
+        expect(pluginManager.serverAddOns.size).toBe(1);
+
+        controlledP.resolve(addOnCleanupMock);
+        await startP1;
+        await startP2;
+
+        expect(loadServerAddOnMock).toBeCalledTimes(1);
+        expect(addOnMock).toBeCalledTimes(1);
+        expect(pluginManager.serverAddOns.size).toBe(1);
+
+        const serverAddOn = pluginManager.serverAddOns.get(pluginName);
+        expect(serverAddOn).toBeInstanceOf(ServerAddOnManager);
+        expect(serverAddOn!.state.is('active')).toBeTruthy();
+      });
+
+      test('concurrent calls to stopServerAddOn stop add-on only once', async () => {
+        const {pluginManager, addOnCleanupMock} = await startServerAddOn(
+          details,
+        );
+
+        const controlledP = createControlledPromise<void>();
+        addOnCleanupMock.mockImplementation(() => controlledP.promise);
+
+        expect(addOnCleanupMock).toBeCalledTimes(0);
+
+        const stopP1 = pluginManager.stopServerAddOn(pluginName, initialOwner);
+        expect(addOnCleanupMock).toBeCalledTimes(1);
+
+        const stopP2 = pluginManager.stopServerAddOn(pluginName, initialOwner);
+        expect(addOnCleanupMock).toBeCalledTimes(1);
+
+        controlledP.resolve();
+        await stopP1;
+        await stopP2;
+
+        expect(addOnCleanupMock).toBeCalledTimes(1);
+      });
+    });
+  });
+});
diff --git a/desktop/flipper-server-core/src/plugins/__tests__/ServerAddOn.node.tsx b/desktop/flipper-server-core/src/plugins/__tests__/ServerAddOn.node.tsx
index 05e8744f7..99cadf0e8 100644
--- a/desktop/flipper-server-core/src/plugins/__tests__/ServerAddOn.node.tsx
+++ b/desktop/flipper-server-core/src/plugins/__tests__/ServerAddOn.node.tsx
@@ -11,34 +11,18 @@ import {ServerAddOnStartDetails} from 'flipper-common';
 import {loadServerAddOn} from '../loadServerAddOn';
 import {ServerAddOn} from '../ServerAddOn';
 import {ServerAddOnModuleToDesktopConnection} from '../ServerAddOnModuleToDesktopConnection';
+import {
+  createControlledPromise,
+  detailsBundled,
+  detailsInstalled,
+  initialOwner,
+  pluginName,
+} from './utils';
 
 jest.mock('../loadServerAddOn');
 const loadServerAddOnMock = loadServerAddOn as jest.Mock;
 
-const createControlledPromise = () => {
-  let resolve!: () => void;
-  let reject!: (reason: unknown) => void;
-  const promise = new Promise<void>((resolveP, rejectP) => {
-    resolve = resolveP;
-    reject = rejectP;
-  });
-  return {
-    promise,
-    resolve,
-    reject,
-  };
-};
-
 describe('ServerAddOn', () => {
-  const pluginName = 'lightSaber';
-  const initialOwner = 'yoda';
-  const detailsBundled: ServerAddOnStartDetails = {
-    isBundled: true,
-  };
-  const detailsInstalled: ServerAddOnStartDetails = {
-    path: '/dagobar/',
-  };
-
   const startServerAddOn = async (details: ServerAddOnStartDetails) => {
     const addOnCleanupMock = jest.fn();
     const addOnMock = jest.fn().mockImplementation(() => addOnCleanupMock);
@@ -91,7 +75,7 @@ describe('ServerAddOn', () => {
     test('stops the add-on when the initial owner is removed', async () => {
       const {serverAddOn, addOnCleanupMock} = await startServerAddOn(details);
 
-      const controlledP = createControlledPromise();
+      const controlledP = createControlledPromise<void>();
       addOnCleanupMock.mockImplementation(() => controlledP.promise);
 
       const removeOwnerRes = serverAddOn.removeOwner(initialOwner);
@@ -109,7 +93,7 @@ describe('ServerAddOn', () => {
       const newOwner = 'luke';
       serverAddOn.addOwner(newOwner);
 
-      const controlledP = createControlledPromise();
+      const controlledP = createControlledPromise<void>();
       addOnCleanupMock.mockImplementation(() => controlledP.promise);
 
       const removeOwnerRes1 = serverAddOn.removeOwner(initialOwner);
@@ -138,7 +122,7 @@ describe('ServerAddOn', () => {
     test('calls stop only once when removeOwner is called twice with the same owner', async () => {
       const {serverAddOn, addOnCleanupMock} = await startServerAddOn(details);
 
-      const controlledP = createControlledPromise();
+      const controlledP = createControlledPromise<void>();
       addOnCleanupMock.mockImplementation(() => controlledP.promise);
 
       const removeOwnerRes1 = serverAddOn.removeOwner(initialOwner);
diff --git a/desktop/flipper-server-core/src/plugins/__tests__/utils.tsx b/desktop/flipper-server-core/src/plugins/__tests__/utils.tsx
new file mode 100644
index 000000000..4b0c5b0d5
--- /dev/null
+++ b/desktop/flipper-server-core/src/plugins/__tests__/utils.tsx
@@ -0,0 +1,33 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @format
+ */
+
+import {ServerAddOnStartDetails} from 'flipper-common';
+
+export const pluginName = 'lightSaber';
+export const initialOwner = 'yoda';
+export const detailsBundled: ServerAddOnStartDetails = {
+  isBundled: true,
+};
+export const detailsInstalled: ServerAddOnStartDetails = {
+  path: '/dagobar/',
+};
+
+export const createControlledPromise = <T,>() => {
+  let resolve!: (...res: T extends void ? [] : [T]) => void;
+  let reject!: (reason: unknown) => void;
+  const promise = new Promise<T>((resolveP, rejectP) => {
+    resolve = resolveP as typeof resolve;
+    reject = rejectP;
+  });
+  return {
+    promise,
+    resolve,
+    reject,
+  };
+};