diff --git a/packages/client-app/internal_packages/sync-health-checker/spec/sync-health-checker-spec.es6 b/packages/client-app/internal_packages/sync-health-checker/spec/sync-health-checker-spec.es6
new file mode 100644
index 000000000..09dfb581a
--- /dev/null
+++ b/packages/client-app/internal_packages/sync-health-checker/spec/sync-health-checker-spec.es6
@@ -0,0 +1,44 @@
+import {ipcRenderer} from 'electron'
+import SyncHealthChecker from '../lib/sync-health-checker'
+
+const requestWithErrorResponse = () => {
+  return {
+    run: async () => {
+      throw new Error('ECONNREFUSED');
+    },
+  }
+}
+
+const activityData = {account1: {time: 1490305104619, activity: ['activity']}}
+
+const requestWithDataResponse = () => {
+  return {
+    run: async () => {
+      return activityData
+    },
+  }
+}
+
+describe('SyncHealthChecker', () => {
+  describe('when the worker window is not available', () => {
+    beforeEach(() => {
+      spyOn(SyncHealthChecker, '_buildRequest').andCallFake(requestWithErrorResponse)
+      spyOn(ipcRenderer, 'send')
+      spyOn(NylasEnv, 'reportError')
+    })
+    it('attempts to restart it', async () => {
+      await SyncHealthChecker._checkSyncHealth();
+      expect(NylasEnv.reportError.calls.length).toEqual(1)
+      expect(ipcRenderer.send.calls[0].args[0]).toEqual('ensure-worker-window')
+    })
+  })
+  describe('when data is returned', () => {
+    beforeEach(() => {
+      spyOn(SyncHealthChecker, '_buildRequest').andCallFake(requestWithDataResponse)
+    })
+    it('stores the data', async () => {
+      await SyncHealthChecker._checkSyncHealth();
+      expect(SyncHealthChecker._lastSyncActivity).toEqual(activityData)
+    })
+  })
+})
diff --git a/packages/client-sync/spec/local-sync-worker/sync-process-manager-spec.es6 b/packages/client-sync/spec/local-sync-worker/sync-process-manager-spec.es6
new file mode 100644
index 000000000..8e9875944
--- /dev/null
+++ b/packages/client-sync/spec/local-sync-worker/sync-process-manager-spec.es6
@@ -0,0 +1,68 @@
+import {IdentityStore} from 'nylas-exports'
+import {createLogger} from '../../src/shared/logger'
+import LocalDatabaseConnector from '../../src/shared/local-database-connector'
+import SyncProcessManager from '../../src/local-sync-worker/sync-process-manager'
+import SyncActivity from '../../src/shared/sync-activity'
+
+describe("SynccProcessManager", () => {
+  beforeEach(async () => {
+    global.Logger = createLogger()
+    spyOn(IdentityStore, 'identity').andReturn(true)
+    const db = await LocalDatabaseConnector.forShared();
+    await db.Account.create({id: 'test-account'})
+  })
+  afterEach(async () => {
+    const db = await LocalDatabaseConnector.forShared();
+    const accounts = db.Account.findAll();
+    return Promise.all(accounts.map((account) => account.destroy()))
+  })
+  describe("when a sync worker is stuck", () => {
+    beforeEach(() => {
+      spyOn(NylasEnv, 'reportError')
+      spyOn(SyncProcessManager, 'removeWorkerForAccountId').andCallThrough()
+      spyOn(SyncProcessManager, 'addWorkerForAccount').andCallThrough()
+      spyOn(SyncActivity, 'getLastSyncActivityForAccount').andReturn({
+        time: Date.now() - 2 * SyncProcessManager.MAX_WORKER_SILENCE_MS,
+        activity: ['activity'],
+      })
+      // Make sure the health check interval isn't automatically started
+      SyncProcessManager._check_health_interval = 1
+    })
+    it("detects it and recovers", async () => {
+      await SyncProcessManager.start()
+      expect(SyncProcessManager.removeWorkerForAccountId.calls.length).toEqual(0)
+      expect(SyncProcessManager.addWorkerForAccount.calls.length).toEqual(1)
+
+      await SyncProcessManager._checkHealth()
+      expect(NylasEnv.reportError.calls.length).toEqual(1)
+      expect(SyncProcessManager.removeWorkerForAccountId.calls.length).toEqual(1)
+      expect(SyncProcessManager.addWorkerForAccount.calls.length).toEqual(2)
+    })
+    it("doesn't have zombie workers come back to life", async () => {
+      await SyncProcessManager.start()
+
+      // Zombify a worker
+      const zombieSync = () => {
+        return new Promise(() => {}) // Never resolves
+      }
+      const zombieWorker = SyncProcessManager.workers()[0]
+      const origSync = zombieWorker.syncNow
+      zombieWorker.syncNow = zombieSync
+      zombieWorker.interrupt()
+      zombieWorker.syncNow()
+
+      // Make sure the worker is discarded by the manager
+      await SyncProcessManager._checkHealth()
+      expect(NylasEnv.reportError.calls.length).toEqual(1)
+      expect(SyncProcessManager.removeWorkerForAccountId.calls.length).toEqual(1)
+      expect(SyncProcessManager.addWorkerForAccount.calls.length).toEqual(2)
+
+      // Try to get the zombie to sync again, check that it doesn't.
+      const lastStart = zombieWorker._syncStart;
+      zombieWorker.syncNow = origSync
+      zombieWorker.interrupt({reason: 'Playing Frankenstein'})
+      await zombieWorker.syncNow()
+      expect(zombieWorker._syncStart).toEqual(lastStart)
+    })
+  })
+})