diff --git a/activities-cancellation-heartbeating/package.json b/activities-cancellation-heartbeating/package.json
index c57d4857..cdeb1bc9 100644
--- a/activities-cancellation-heartbeating/package.json
+++ b/activities-cancellation-heartbeating/package.json
@@ -28,13 +28,16 @@
     "@temporalio/workflow": "^1.11.6"
   },
   "devDependencies": {
+    "@temporalio/testing": "^1.11.7",
     "@tsconfig/node18": "^18.2.4",
+    "@types/mocha": "^10.0.10",
     "@types/node": "^22.9.1",
     "@typescript-eslint/eslint-plugin": "^8.18.0",
     "@typescript-eslint/parser": "^8.18.0",
     "eslint": "^8.57.1",
     "eslint-config-prettier": "^9.1.0",
     "eslint-plugin-deprecation": "^3.0.0",
+    "mocha": "^11.1.0",
     "nodemon": "^3.1.7",
     "prettier": "^3.4.2",
     "ts-node": "^10.9.2",
diff --git a/activities-cancellation-heartbeating/src/activities-test.ts b/activities-cancellation-heartbeating/src/activities-test.ts
new file mode 100644
index 00000000..11db2ebe
--- /dev/null
+++ b/activities-cancellation-heartbeating/src/activities-test.ts
@@ -0,0 +1,52 @@
+import { MockActivityEnvironment } from '@temporalio/testing';
+import * as assert from 'node:assert';
+import { CancelledFailure } from '@temporalio/workflow';
+import { ActivityExecutionDetails, myLongRunningActivity } from './activities';
+
+describe('LongRunningActivity Test', function() {
+
+  describe('when background heartbeating', function() {
+    let testEnv: MockActivityEnvironment
+    beforeEach(async function() {
+      testEnv = new MockActivityEnvironment({
+        startToCloseTimeoutMs: 2000,
+        heartbeatTimeoutMs: 200,
+        heartbeatDetails: 0,
+      })
+    })
+    it('should sent details back', async function() {
+      const actual: ActivityExecutionDetails = await testEnv.run(myLongRunningActivity)
+      assert.equal(actual.heartbeatsReported, 18)
+    })
+  })
+  describe('when background heartbeating received cancellation notice', function() {
+    let testEnv: MockActivityEnvironment
+    beforeEach(async function() {
+      testEnv = new MockActivityEnvironment({
+        startToCloseTimeoutMs: 2000,
+        heartbeatTimeoutMs: 200,
+        heartbeatDetails: 0,
+      })
+    })
+    it('should sent details back', async function() {
+
+      const cancelPromise= async (): Promise<void> => {
+        return new Promise(resolve => {
+          setTimeout(() => {}, 200)
+          testEnv.cancel('verify CancelledFailure bubbles up')
+          resolve()
+        })
+      }
+      const runPromise= async (): Promise<ActivityExecutionDetails>  => {
+        return await testEnv.run(myLongRunningActivity)
+      }
+
+      const actual = await Promise.allSettled([cancelPromise(), runPromise()])
+      assert.ok(actual[1])
+      assert.equal("fulfilled", actual[1].status)
+      // eslint-disable-next-line @typescript-eslint/ban-ts-comment
+      // @ts-ignore
+      assert.ok(actual[1].value.err instanceof CancelledFailure)
+    })
+  })
+})
\ No newline at end of file
diff --git a/activities-cancellation-heartbeating/src/activities.ts b/activities-cancellation-heartbeating/src/activities.ts
index 956b11b7..4161ee5c 100644
--- a/activities-cancellation-heartbeating/src/activities.ts
+++ b/activities-cancellation-heartbeating/src/activities.ts
@@ -1,5 +1,13 @@
 // @@@SNIPSTART typescript-activity-fake-progress
-import { activityInfo, log, sleep, CancelledFailure, heartbeat } from '@temporalio/activity';
+import {
+  activityInfo,
+  log,
+  sleep,
+  CancelledFailure,
+  heartbeat,
+  Context,
+  ApplicationFailure
+} from '@temporalio/activity';
 
 export async function fakeProgress(sleepIntervalMs = 1000): Promise<void> {
   try {
@@ -22,3 +30,90 @@ export async function fakeProgress(sleepIntervalMs = 1000): Promise<void> {
   }
 }
 // @@@SNIPEND
+
+// @@@SNIPSTART typescript-activity-long-running
+export interface ActivityExecutionDetails {
+  heartbeatsReported: number
+  mainOperationResult: string | undefined
+  err: Error | undefined
+}
+export async function myLongRunningActivity(): Promise<ActivityExecutionDetails> {
+  const ctx = Context.current()
+  const details: ActivityExecutionDetails = {
+    heartbeatsReported: ctx.info.heartbeatDetails || 0,
+    mainOperationResult:  undefined,
+    err: undefined
+  }
+  const logger = ctx.log
+  const heartbeatTimeoutMs = ctx.info.heartbeatTimeoutMs
+  if(!heartbeatTimeoutMs) {
+    throw ApplicationFailure.nonRetryable("heartbeat is required", "ERR_MISSING_HEARTBEAT_TIMEOUT")
+  }
+  const heartbeatInterval = heartbeatTimeoutMs / 2
+
+  // mainOperation is the "real" work we are doing in the Activity
+  async function mainOperation(): Promise<string> {
+    const successMessage = 'operation successful'
+    // use startToClose as basis for overall ops timeouts
+    const timeout = ctx.info.startToCloseTimeoutMs - 100
+
+    return new Promise((resolve) => {
+      logger.debug('simulating operation for (ms)', {timeout})
+      // this simulates some lengthy operation like a report generation or API call
+      // we avoid using `sleep` so that the operation won't receive a CancelledFailure directly
+      setTimeout(() => {
+        // capture the operation result
+        details.mainOperationResult = successMessage
+        resolve(successMessage)
+      }, timeout)
+    })
+  }
+  // doHeartbeat creates the regular looped heartbeat we need
+  async function doHeartbeat():Promise<void> {
+    // noinspection InfiniteLoopJS
+    logger.debug('heartbeating every (ms)',{heartbeatInterval})
+    return new Promise((resolve, reject) => {
+      return (async function periodic() {
+        while(!details.err && !details.mainOperationResult) {
+          try {
+            // this will return a CancelledFailure if the server replies as such
+            // since we arent catching it it will bubble up to the main operation
+            await sleep(heartbeatInterval)
+            // you can pass in details to the heartbeat if you like to preserve "where" you are
+            heartbeat(++details.heartbeatsReported)
+          } catch (err) {
+            // demonstrate how to test for cancellation
+            if(err instanceof CancelledFailure) {
+              logger.error('cancelling heartbeat due to cancellation', {err})
+            }
+            logger.error('heartbeat received failure', {err})
+            reject(err)
+            // exit loop
+            throw err
+          }
+        }
+      })()
+    })
+    }
+  // _race_ the heartbeat and mainOperation so that any failure from either mainOperation or heartbeat to arrive
+  // will resolve the Promise collection. This is important for the CancelledFailure to be handled appropriately.
+  // Cancellation of the process inside the mainOperation is outside the scope of this sample, but
+  // you might need to abort processes explicitly upon Cancellation from Workflow.
+  // For example, with https://developer.mozilla.org/en-US/docs/Web/API/AbortController
+  try {
+    const result: string | void =  await Promise.race([doHeartbeat(), mainOperation()])
+    logger.debug('received result', {result})
+  } catch (err) {
+    logger.error('Activity received error', {err})
+    details.err = err as Error
+    if(err instanceof CancelledFailure) {
+      // we could rethrow the error here or ignore it (as we have done here)
+      // throw it. log it. sorted. :)
+    }
+
+  }
+  return details
+}
+
+
+// @@@SNIPEND
\ No newline at end of file