diff --git a/tracker/tracker/src/webworker/BatchWriter.unit.test.ts b/tracker/tracker/src/webworker/BatchWriter.unit.test.ts
new file mode 100644
index 000000000..e9f039988
--- /dev/null
+++ b/tracker/tracker/src/webworker/BatchWriter.unit.test.ts
@@ -0,0 +1,95 @@
+import BatchWriter from './BatchWriter'
+import * as Messages from '../common/messages.gen.js'
+import { describe, expect, test, jest, beforeEach, afterEach } from '@jest/globals'
+import Message from '../common/messages.gen.js'
+
+describe('BatchWriter', () => {
+  let onBatchMock: (b: Uint8Array) => void
+  let batchWriter: BatchWriter
+
+  beforeEach(() => {
+    onBatchMock = jest.fn()
+    batchWriter = new BatchWriter(1, 123456789, 'example.com', onBatchMock)
+  })
+
+  afterEach(() => {
+    jest.clearAllMocks()
+  })
+
+  test('constructor initializes BatchWriter instance', () => {
+    expect(batchWriter['pageNo']).toBe(1)
+    expect(batchWriter['timestamp']).toBe(123456789)
+    expect(batchWriter['url']).toBe('example.com')
+    expect(batchWriter['onBatch']).toBe(onBatchMock)
+    expect(batchWriter['nextIndex']).toBe(0)
+    expect(batchWriter['beaconSize']).toBe(200000)
+    expect(batchWriter['encoder']).toBeDefined()
+    expect(batchWriter['strDict']).toBeDefined()
+    expect(batchWriter['sizeBuffer']).toHaveLength(3)
+    expect(batchWriter['isEmpty']).toBe(true)
+  })
+
+  test('writeType writes the type of the message', () => {
+    const message = [Messages.Type.BatchMetadata, 1, 2, 3, 4, 'example.com']
+    const result = batchWriter['writeType'](message as Message)
+    expect(result).toBe(true)
+  })
+
+  test('writeFields encodes the message fields', () => {
+    const message = [Messages.Type.BatchMetadata, 1, 2, 3, 4, 'example.com']
+    const result = batchWriter['writeFields'](message as Message)
+    expect(result).toBe(true)
+  })
+
+  test('writeSizeAt writes the size at the given offset', () => {
+    batchWriter['writeSizeAt'](100, 0)
+    expect(batchWriter['sizeBuffer']).toEqual(new Uint8Array([100, 0, 0]))
+    expect(batchWriter['encoder']['data'].slice(0, 3)).toEqual(new Uint8Array([100, 0, 0]))
+  })
+
+  test('prepare prepares the BatchWriter for writing', () => {
+    // TODO
+  })
+
+  test('writeWithSize writes the message with its size', () => {
+    const message = [Messages.Type.BatchMetadata, 1, 2, 3, 4, 'example.com']
+    const result = batchWriter['writeWithSize'](message as Message)
+    expect(result).toBe(true)
+  })
+
+  test('setBeaconSizeLimit sets the beacon size limit', () => {
+    batchWriter['setBeaconSizeLimit'](500000)
+    expect(batchWriter['beaconSizeLimit']).toBe(500000)
+  })
+
+  test('Set note attribute tries to use dictionary', () => {
+    const spyOnStrGetKey = jest.spyOn(batchWriter['strDict'], 'getKey')
+    // @ts-ignore
+    batchWriter['writeMessage']([Messages.Type.SetNodeAttribute, 1, 'name', 'value'])
+    expect(spyOnStrGetKey).toHaveBeenCalledTimes(2)
+    expect(spyOnStrGetKey).toHaveBeenCalledWith('name')
+    expect(spyOnStrGetKey).toHaveBeenCalledWith('value')
+  })
+
+  test('writeMessage writes the given message', () => {
+    const message = [Messages.Type.Timestamp, 987654321]
+    // @ts-ignore
+    batchWriter['writeWithSize'] = jest.fn().mockReturnValue(true)
+    batchWriter['writeMessage'](message as Message)
+    expect(batchWriter['writeWithSize']).toHaveBeenCalledWith(message)
+  })
+
+  test('finaliseBatch flushes the encoder and calls onBatch', () => {
+    const flushSpy = jest.spyOn(batchWriter['encoder'], 'flush')
+    batchWriter['isEmpty'] = false
+    batchWriter['finaliseBatch']()
+    expect(flushSpy).toHaveBeenCalled()
+    expect(onBatchMock).toHaveBeenCalled()
+  })
+
+  test('clean resets the encoder', () => {
+    const cleanSpy = jest.spyOn(batchWriter['encoder'], 'reset')
+    batchWriter['clean']()
+    expect(cleanSpy).toHaveBeenCalled()
+  })
+})