diff --git a/package.json b/package.json
index ccf7d79..93ba999 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "contentful-sdk-core",
-  "version": "0.0.1-determined-by-semantic-release",
+  "version": "0.0.0-determined-by-semantic-release",
   "description": "Core modules for the Contentful JS SDKs",
   "homepage": "https://www.contentful.com/developers/docs/javascript/",
   "main": "dist/index.js",
@@ -23,9 +23,9 @@
     "build": "npm run clean && npm run build:types && npm run build:js",
     "lint": "eslint src test --ext '.ts,.js'",
     "pretest": "npm run lint",
-    "test": "tsdx test",
-    "test:watch": "tsdx test --watch",
-    "test:cover": "tsdx test --coverage",
+    "test": "jest",
+    "test:watch": "jest --watch",
+    "test:cover": "jest --coverage",
     "browser-coverage": "npm run test:cover && opener coverage/lcov-report/index.html",
     "prepublish": "in-publish && npm run build || not-in-publish",
     "semantic-release": "semantic-release",
@@ -41,7 +41,7 @@
     "bin"
   ],
   "engines": {
-    "node": ">=6"
+    "node": ">=12"
   },
   "dependencies": {
     "fast-copy": "^2.1.0",
@@ -64,13 +64,14 @@
     "@semantic-release/npm": "^7.1.3",
     "@semantic-release/release-notes-generator": "^9.0.3",
     "@types/chai": "^4.2.21",
+    "@types/jest": "^27.4.0",
     "@types/lodash.isplainobject": "^4.0.6",
     "@types/lodash.isstring": "^4.0.6",
     "@types/qs": "^6.9.5",
-    "@typescript-eslint/eslint-plugin": "4.33.0",
-    "@typescript-eslint/parser": "4.31.2",
-    "axios": "^0.21.0",
-    "axios-mock-adapter": "^1.15.0",
+    "@typescript-eslint/eslint-plugin": "^5.11.0",
+    "@typescript-eslint/parser": "^5.11.0",
+    "axios": "^0.25.0",
+    "axios-mock-adapter": "^1.20.0",
     "babel-eslint": "^10.1.0",
     "bundlesize": "^0.18.1",
     "chai": "^4.3.4",
@@ -86,6 +87,7 @@
     "eslint-plugin-standard": "^5.0.0",
     "husky": "^7.0.0",
     "in-publish": "^2.0.0",
+    "jest": "^27.5.1",
     "lint-staged": "^12.0.2",
     "mkdirp": "^1.0.4",
     "moxios": "^0.4.0",
@@ -97,9 +99,9 @@
     "rollup": "^2.34.0",
     "rollup-plugin-babel": "^4.4.0",
     "semantic-release": "^17.0.7",
-    "tsdx": "^0.14.1",
+    "ts-jest": "^27.1.3",
     "tslib": "^2.0.3",
-    "typescript": "3.9.10"
+    "typescript": "^4.5.5"
   },
   "bundlesize": [
     {
diff --git a/src/create-http-client.ts b/src/create-http-client.ts
index 277ab79..5c3db7c 100644
--- a/src/create-http-client.ts
+++ b/src/create-http-client.ts
@@ -1,3 +1,4 @@
+import { AxiosRequestHeaders } from 'axios'
 import copy from 'fast-copy'
 import qs from 'qs'
 import type { AxiosStatic } from 'axios'
@@ -38,7 +39,7 @@ export default function createHttpClient(
       console.log(`[${level}] ${data}`)
     },
     // Passed to axios
-    headers: {} as Record<string, unknown>,
+    headers: {} as AxiosRequestHeaders,
     httpAgent: false as const,
     httpsAgent: false as const,
     timeout: 30000,
diff --git a/src/error-handler.ts b/src/error-handler.ts
index ba01932..f587554 100644
--- a/src/error-handler.ts
+++ b/src/error-handler.ts
@@ -15,7 +15,7 @@ export default function errorHandler(errorResponse: AxiosError): never {
 
   // Obscure the Management token
   if (config && config.headers && config.headers['Authorization']) {
-    const token = `...${config.headers['Authorization'].substr(-5)}`
+    const token = `...${config.headers['Authorization'].toString().substr(-5)}`
     config.headers['Authorization'] = `Bearer ${token}`
   }
 
diff --git a/src/to-plain-object.ts b/src/to-plain-object.ts
index 734890e..46ac8a0 100644
--- a/src/to-plain-object.ts
+++ b/src/to-plain-object.ts
@@ -6,14 +6,7 @@ import copy from 'fast-copy'
  * @param data - Any plain JSON response returned from the API
  * @return Enhanced object with toPlainObject method
  */
-export default function toPlainObject<T = Record<string, unknown>, R = T>(
-  data: T
-): T & {
-  /**
-   * Returns this entity as a plain JS object
-   */
-  toPlainObject(): R
-} {
+export default function toPlainObject(data: unknown) {
   return Object.defineProperty(data, 'toPlainObject', {
     enumerable: false,
     configurable: false,
diff --git a/src/types.ts b/src/types.ts
index f16f74b..88826c2 100644
--- a/src/types.ts
+++ b/src/types.ts
@@ -1,5 +1,6 @@
 /* eslint-disable @typescript-eslint/no-explicit-any */
 
+import { AxiosRequestHeaders } from 'axios'
 import type {
   AxiosInstance as OriginalAxiosInstance,
   AxiosRequestConfig,
@@ -61,7 +62,7 @@ export type CreateHttpClientParams = {
   logHandler?: DefaultOptions['logHandler']
 
   /** Optional additional headers */
-  headers?: Record<string, unknown>
+  headers?: AxiosRequestHeaders
 
   defaultHostname?: string
 
diff --git a/test/unit/create-http-client-integration.spec.ts b/test/unit/create-http-client-integration.spec.ts
index 538e945..af27b76 100644
--- a/test/unit/create-http-client-integration.spec.ts
+++ b/test/unit/create-http-client-integration.spec.ts
@@ -21,7 +21,7 @@ it('should retrieve token asynchronously', async () => {
   expect(instance.defaults.headers.Authorization).not.toBeDefined()
 
   await instance.get('/test-endpoint')
-  expect(mock.history.get[0].headers.Authorization).toEqual('Bearer async-token')
+  expect(mock.history.get[0].headers?.Authorization).toEqual('Bearer async-token')
 })
 
 describe('custom interceptors', () => {
@@ -45,10 +45,10 @@ describe('custom interceptors', () => {
     mock.onGet('/test-endpoint').replyOnce(200)
 
     await instance.get('/test-endpoint')
-    expect(mock.history.get[0].headers['custom-header']).toEqual('custom-header-value')
+    expect(mock.history.get[0].headers?.['custom-header']).toEqual('custom-header-value')
   })
 
-  it('is able to intercept responce codes', async () => {
+  it('is able to intercept response codes', async () => {
     let accessToken = 'invalid-token'
 
     const refreshToken = () => {
@@ -63,6 +63,8 @@ describe('custom interceptors', () => {
         if (error.response.status === 403 && !originalRequest._retry403) {
           originalRequest._retry403 = true
           const newToken = await refreshToken()
+          // eslint-disable-next-line @typescript-eslint/ban-ts-comment
+          // @ts-ignore
           axios.defaults.headers.Authorization = 'Bearer ' + newToken
           return instance(originalRequest)
         }
@@ -75,7 +77,7 @@ describe('custom interceptors', () => {
 
     await instance.get('/test-endpoint')
 
-    expect(mock.history.get[0].headers.Authorization).toEqual('Bearer invalid-token')
-    expect(mock.history.get[1].headers.Authorization).toEqual('Bearer valid-token')
+    expect(mock.history.get[0].headers?.Authorization).toEqual('Bearer invalid-token')
+    expect(mock.history.get[1].headers?.Authorization).toEqual('Bearer valid-token')
   })
 })
diff --git a/test/unit/create-http-client-test.spec.ts b/test/unit/create-http-client-test.spec.ts
index f2ce0e0..cb464a9 100644
--- a/test/unit/create-http-client-test.spec.ts
+++ b/test/unit/create-http-client-test.spec.ts
@@ -1,3 +1,5 @@
+/* eslint-disable @typescript-eslint/no-explicit-any */
+
 import createHttpClient from '../../src/create-http-client'
 
 import axios, { AxiosAdapter } from 'axios'
@@ -84,25 +86,25 @@ it('Calls axios based on passed headers', () => {
 
   const [callConfig] = mockedAxios.create.mock.calls[0]
   expect(callConfig?.baseURL)
-  expect(callConfig?.headers['X-Custom-Header']).toEqual('example')
-  expect(callConfig?.headers.Authorization).toEqual('Basic customAuth')
+  expect(callConfig?.headers?.['X-Custom-Header']).toEqual('example')
+  expect(callConfig?.headers?.Authorization).toEqual('Basic customAuth')
 })
 
-it('Calls axios with reques/response logger', () => {
-  const requestloggerStub = jest.fn()
-  const responseloggerStub = jest.fn()
+it('Calls axios with request/response logger', () => {
+  const requestLoggerStub = jest.fn()
+  const responseLoggerStub = jest.fn()
   createHttpClient(axios, {
     accessToken: 'clientAccessToken',
     host: 'contentful.com',
     insecure: true,
-    requestLogger: requestloggerStub,
-    responseLogger: responseloggerStub,
+    requestLogger: requestLoggerStub,
+    responseLogger: responseLoggerStub,
   })
 
   const [callConfig] = mockedAxios.create.mock.calls[0]
   expect(callConfig?.baseURL).toEqual('http://contentful.com:80/spaces/')
-  expect(requestloggerStub).not.toHaveBeenCalled()
-  expect(responseloggerStub).not.toHaveBeenCalled()
+  expect(requestLoggerStub).not.toHaveBeenCalled()
+  expect(responseLoggerStub).not.toHaveBeenCalled()
 })
 
 it('Fails with missing access token', () => {
@@ -111,7 +113,7 @@ it('Fails with missing access token', () => {
     createHttpClient(axios, {
       logHandler: logHandlerStub,
     })
-  } catch (err) {
+  } catch (err: any) {
     expect(err instanceof TypeError).toBeTruthy()
     expect(err.message).toEqual('Expected parameter accessToken')
     expect(logHandlerStub).toHaveBeenCalledTimes(1)
diff --git a/test/unit/error-handler-test.spec.ts b/test/unit/error-handler-test.spec.ts
index 9793ca2..588002b 100644
--- a/test/unit/error-handler-test.spec.ts
+++ b/test/unit/error-handler-test.spec.ts
@@ -1,3 +1,5 @@
+/* eslint-disable @typescript-eslint/no-explicit-any */
+
 import errorHandler from '../../src/error-handler'
 import { errorMock } from './mocks'
 import { expect } from 'chai'
@@ -21,7 +23,7 @@ describe('A errorHandler', () => {
 
     try {
       errorHandler(error)
-    } catch (err) {
+    } catch (err: any) {
       const parsedMessage = JSON.parse(err.message)
       expect(err.name).equals('SpecificError', 'error name')
       expect(parsedMessage.request.url).equals('requesturl', 'request url')
@@ -46,7 +48,7 @@ describe('A errorHandler', () => {
 
     try {
       errorHandler(error)
-    } catch (err) {
+    } catch (err: any) {
       const parsedMessage = JSON.parse(err.message)
       expect(err.name).equals('500 Internal', 'error name defaults to status code and text')
       expect(parsedMessage.request.url).equals('requesturl', 'request url')
@@ -61,7 +63,7 @@ describe('A errorHandler', () => {
 
     try {
       errorHandler(error)
-    } catch (err) {
+    } catch (err: any) {
       const parsedMessage = JSON.parse(err.message)
       expect(err.name).equals(
         '500 Everything is on fire',
@@ -79,7 +81,7 @@ describe('A errorHandler', () => {
 
     try {
       errorHandler(responseError)
-    } catch (err) {
+    } catch (err: any) {
       const parsedMessage = JSON.parse(err.message)
       expect(parsedMessage.request.headers.Authorization).equals(
         'Bearer ...token',
@@ -105,7 +107,7 @@ describe('A errorHandler', () => {
 
     try {
       errorHandler(requestError)
-    } catch (err) {
+    } catch (err: any) {
       expect(err.config.headers.Authorization).equals('Bearer ...token', 'Obscures token')
     }
   })
diff --git a/test/unit/rate-limit-test.spec.ts b/test/unit/rate-limit-test.spec.ts
index 2b30a03..fd603f8 100644
--- a/test/unit/rate-limit-test.spec.ts
+++ b/test/unit/rate-limit-test.spec.ts
@@ -1,3 +1,5 @@
+/* eslint-disable @typescript-eslint/no-explicit-any */
+
 import axios from 'axios'
 import MockAdapter from 'axios-mock-adapter'
 
@@ -89,7 +91,7 @@ it('Retry on network error', async () => {
 
   try {
     await client.get('/rate-limit-me')
-  } catch (error) {
+  } catch (error: any) {
     // logs two attempts, one initial and one retry
     expect(error.attempts).toEqual(2)
   }
@@ -105,7 +107,7 @@ it('no retry when automatic handling flag is disabled', async () => {
   expect.assertions(6)
   try {
     await client.get('/rate-limit-me')
-  } catch (error) {
+  } catch (error: any) {
     expect(error.response.status).toEqual(500)
     expect(error.response.headers['x-contentful-request-id']).toEqual(3)
     expect(error.response.data).toEqual('Mocked 500 Error')
@@ -124,7 +126,7 @@ it('Should Fail if it hits maxRetries', async () => {
   expect.assertions(5)
   try {
     await client.get('/error')
-  } catch (error) {
+  } catch (error: any) {
     // returned error since maxRetries was reached
     expect(error.response.data).toEqual('error attempt #2')
     expect(logHandlerStub).toHaveBeenCalledTimes(1)
@@ -144,7 +146,7 @@ it('Retry on responses when X-Contentful-Request-Id header is missing', async ()
 
   try {
     await client.get('/error')
-  } catch (error) {
+  } catch (error: any) {
     expect(error.response.data).toEqual('error attempt 2')
     expect(logHandlerStub).toHaveBeenCalledTimes(1)
     expect(logHandlerStub.mock.calls[0][0]).toEqual('warning')
@@ -161,7 +163,7 @@ it('Rejects errors with strange status codes', async () => {
   expect.assertions(2)
   try {
     await client.get('/error')
-  } catch (error) {
+  } catch (error: any) {
     expect(error.response.data).toEqual('error attempt')
     // did not log anything
     expect(logHandlerStub).toBeCalledTimes(0)