diff --git a/package.json b/package.json
index d5c2fff..7fd1aa6 100644
--- a/package.json
+++ b/package.json
@@ -38,19 +38,19 @@
   },
   "dependencies": {
     "acquerello": "^1.0.0",
-    "hdr-histogram-js": "^2.0.1",
+    "hdr-histogram-js": "^3.0.0",
     "table": "^6.7.1"
   },
   "devDependencies": {
-    "@cowtech/eslint-config": "^7.14.5",
-    "@cowtech/esm-package-utils": "^0.9.1",
-    "@types/node": "^16.6.1",
+    "@cowtech/eslint-config": "^8.0.1",
+    "@cowtech/esm-package-utils": "^0.9.3",
+    "@types/node": "^17.0.2",
     "@types/sinon": "^10.0.2",
     "@types/tap": "^15.0.5",
     "c8": "^7.8.0",
     "prettier": "^2.3.2",
     "proxyquire": "^2.1.3",
-    "sinon": "^11.1.2",
+    "sinon": "^12.0.1",
     "tap": "^15.0.9",
     "ts-node": "^10.2.0",
     "typescript": "^4.3.5"
diff --git a/src/index.ts b/src/index.ts
index 3ba38ea..6409c32 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -1,7 +1,7 @@
 'use strict'
 
 import { isMainThread, Worker, workerData } from 'worker_threads'
-import { Callback, Context, defaultOptions, Options, PrintOptions, Result, Results, runnerPath, Tests } from './models'
+import { Callback, Context, defaultOptions, Options, PrintOptions, Results, runnerPath, Tests } from './models'
 import { printResults } from './print'
 
 type PromiseResolver<T> = (value: T) => void
@@ -42,7 +42,7 @@ function run(context: Context): void {
     }
   })
 
-  worker.on('error', (error: Error) => {
+  worker.on('error', error => {
     context.results[name] = {
       success: false,
       error,
@@ -60,7 +60,7 @@ function run(context: Context): void {
     scheduleNextTest(context)
   })
 
-  worker.on('message', (result: Result) => {
+  worker.on('message', result => {
     context.results[name] = result
     context.current++
 
@@ -96,7 +96,7 @@ export function cronometro(
   let callback = cb as (err: Error | null, results?: Results) => void
 
   if (!callback) {
-    promise = new Promise<Results>((resolve: PromiseResolver<Results>, reject: PromiseRejecter) => {
+    promise = new Promise<Results>((resolve, reject) => {
       promiseResolve = resolve
       promiseReject = reject
     })
diff --git a/src/models.ts b/src/models.ts
index e9ca9cd..487ab01 100644
--- a/src/models.ts
+++ b/src/models.ts
@@ -29,7 +29,7 @@ export interface Test {
   after?: SetupFunction
 }
 
-export type Callback = ((err: Error | null) => void) | ((err: null, results: Results) => any)
+export type Callback = (err: Error | null, results: Results) => any
 
 export interface Percentiles {
   [key: string]: number
diff --git a/src/print.ts b/src/print.ts
index 559af00..55f1d4c 100644
--- a/src/print.ts
+++ b/src/print.ts
@@ -1,6 +1,6 @@
 import { clean, colorize } from 'acquerello'
 import { table } from 'table'
-import { Result, Results } from './models'
+import { Results } from './models'
 
 const styles = ['red', 'green', 'yellow', 'blue', 'magenta', 'cyan', 'white', 'gray']
 
@@ -29,8 +29,8 @@ export function printResults(results: Results, colors: boolean, compare: boolean
   let standardErrorPadding = 0
 
   const entries: Array<PrintInfo> = Object.entries(results)
-    .sort((a: [string, Result], b: [string, Result]) => (!a[1].success ? -1 : b[1].mean - a[1].mean))
-    .map(([name, result]: [string, Result]) => {
+    .sort((a, b) => (!a[1].success ? -1 : b[1].mean - a[1].mean))
+    .map(([name, result]) => {
       if (!result.success) {
         return {
           name,
@@ -72,7 +72,7 @@ export function printResults(results: Results, colors: boolean, compare: boolean
 
   let currentColor = 0
 
-  const rows: Array<Array<string>> = entries.map((entry: PrintInfo) => {
+  const rows: Array<Array<string>> = entries.map(entry => {
     if (entry.error) {
       const row = [
         styler(`{{gray}}${entry.name}{{-}}`),
diff --git a/src/runner.ts b/src/runner.ts
index b0e8ab5..c4fa336 100644
--- a/src/runner.ts
+++ b/src/runner.ts
@@ -1,10 +1,6 @@
 import { isMainThread, parentPort, workerData } from 'worker_threads'
 import { runWorker } from './worker'
 
-interface TsNodeModule {
-  register: (options: object) => void
-}
-
 if (isMainThread) {
   throw new Error('Do not run this file as main script.')
 }
@@ -17,7 +13,7 @@ if (workerData.path.endsWith('.ts')) {
   const instance = Symbol.for('ts-node.register.instance')
 
   if (!(instance in process)) {
-    chain = import('ts-node').then(({ register }: TsNodeModule) => {
+    chain = import('ts-node').then(({ register }) => {
       register({ project: process.env.TS_NODE_PROJECT })
     })
   }
@@ -28,7 +24,7 @@ chain
   .then(() => {
     return import(workerData.path)
   })
-  .then((module: any) => {
+  .then(module => {
     if (typeof module === 'function') {
       return module()
     } else if (typeof module.default === 'function') {
@@ -37,9 +33,9 @@ chain
   })
   .then(() => {
     // Run the worker
-    runWorker(workerData, (value: any) => parentPort!.postMessage(value), process.exit)
+    runWorker(workerData, value => parentPort!.postMessage(value), process.exit)
   })
-  .catch((e: Error) => {
+  .catch(e => {
     process.nextTick(() => {
       throw e
     })
diff --git a/src/worker.ts b/src/worker.ts
index 95f7ded..cbf7a3f 100644
--- a/src/worker.ts
+++ b/src/worker.ts
@@ -63,7 +63,7 @@ function handleTestIteration(context: TestContext, error?: Error | null): void {
       max: histogram.maxValue,
       mean: histogram.mean,
       stddev: stdDev,
-      percentiles: percentiles.reduce((accu: Percentiles, percentile: number) => {
+      percentiles: percentiles.reduce((accu: Percentiles, percentile) => {
         accu[percentile] = histogram.getValueAtPercentile(percentile)
         return accu
       }, {}),
diff --git a/test/asyncImport.test.ts b/test/asyncImport.test.ts
index 015dcc6..8303e9f 100644
--- a/test/asyncImport.test.ts
+++ b/test/asyncImport.test.ts
@@ -4,10 +4,8 @@ import t from 'tap'
 import { isMainThread } from 'worker_threads'
 import { cronometro, percentiles } from '../src'
 
-type Test = typeof t
-
 async function main(): Promise<void> {
-  await new Promise((resolve: (value: unknown) => void) => setTimeout(resolve, 100))
+  await new Promise(resolve => setTimeout(resolve, 100))
 
   if (!isMainThread) {
     cronometro(
@@ -23,7 +21,7 @@ async function main(): Promise<void> {
       () => false
     )
   } else {
-    t.only('Collecting results', async (t: Test) => {
+    t.only('Collecting results', async t => {
       const results = await cronometro(
         {
           single() {
diff --git a/test/errorHandling.test.ts b/test/errorHandling.test.ts
index 26a1805..b12c7d5 100644
--- a/test/errorHandling.test.ts
+++ b/test/errorHandling.test.ts
@@ -4,8 +4,6 @@ import t from 'tap'
 import { isMainThread } from 'worker_threads'
 import { cronometro, percentiles } from '../src'
 
-type Test = typeof t
-
 if (!isMainThread) {
   cronometro(
     {
@@ -19,7 +17,7 @@ if (!isMainThread) {
     () => false
   )
 } else {
-  t.test('Errored tests handling', async (t: Test) => {
+  t.test('Errored tests handling', async t => {
     const results = await cronometro(
       {
         single() {
@@ -59,11 +57,11 @@ if (!isMainThread) {
     t.strictSame(results.multiple.percentiles, {})
   })
 
-  t.test('Runner cannot be run in main thread', async (t: Test) => {
+  t.test('Runner cannot be run in main thread', async t => {
     await t.rejects(import('../src/runner'), { message: 'Do not run this file as main script.' })
   })
 
-  t.only('Runner reports setup errors', async (t: Test) => {
+  t.only('Runner reports setup errors', async t => {
     const results = await cronometro(
       {
         notDefined() {
diff --git a/test/fixture/sample.ts b/test/fixture/sample.ts
index e4e8e3d..af7f308 100644
--- a/test/fixture/sample.ts
+++ b/test/fixture/sample.ts
@@ -1,5 +1,4 @@
 import cronometro from '../../dist'
-import { Results } from '../../src'
 
 const pattern = /[123]/g
 const replacements: { [key: string]: string } = { 1: 'a', 2: 'b', 3: 'c' }
@@ -11,14 +10,14 @@ const subject =
 cronometro(
   {
     single() {
-      subject.replace(pattern, (m: string) => replacements[m])
+      subject.replace(pattern, m => replacements[m])
     },
     multiple() {
       subject.replace(/1/g, 'a').replace(/2/g, 'b').replace(/3/g, 'c')
     }
   },
   { iterations: 5, errorThreshold: 0, print: { compare: true }, warmup: true },
-  (_err: Error | null, results: Results) => {
+  (_, results) => {
     console.log(JSON.stringify(results, null, 2))
   }
 )
diff --git a/test/genericErrorHandling.test.ts b/test/genericErrorHandling.test.ts
index 1f635f3..7bcb66e 100644
--- a/test/genericErrorHandling.test.ts
+++ b/test/genericErrorHandling.test.ts
@@ -4,12 +4,10 @@ import t from 'tap'
 import { isMainThread } from 'worker_threads'
 import { cronometro } from '../src'
 
-type Test = typeof t
-
 if (!isMainThread) {
   cronometro(undefined as any, () => false)
 } else {
-  t.test('Generic error handling', async (t: Test) => {
+  t.test('Generic error handling', async t => {
     const results = await cronometro(
       {
         single() {
diff --git a/test/optionsValidation.test.ts b/test/optionsValidation.test.ts
index 90c9f5f..b193eac 100644
--- a/test/optionsValidation.test.ts
+++ b/test/optionsValidation.test.ts
@@ -3,9 +3,7 @@
 import t from 'tap'
 import { cronometro } from '../src'
 
-type Test = typeof t
-
-t.test('Options validation', async (t: Test) => {
+t.test('Options validation', async t => {
   await t.rejects(
     () =>
       cronometro(
@@ -34,7 +32,7 @@ t.test('Options validation', async (t: Test) => {
       }
     },
     { errorThreshold: -1 },
-    (err: Error | null) => {
+    err => {
       t.type(err, 'Error')
       t.equal(err!.message, 'The errorThreshold option must be a number between 0 and 100.')
     }
diff --git a/test/print.test.ts b/test/print.test.ts
index 34db04b..e695af6 100644
--- a/test/print.test.ts
+++ b/test/print.test.ts
@@ -3,11 +3,9 @@
 import sinon from 'sinon'
 import t from 'tap'
 import { isMainThread } from 'worker_threads'
-import { cronometro, defaultOptions, percentiles, Results } from '../src'
+import { cronometro, defaultOptions, percentiles } from '../src'
 import { setLogger } from '../src/print'
 
-type Test = typeof t
-
 function removeStyle(source: string): string {
   // eslint-disable-next-line no-control-regex
   return source.replace(/\x1b\[\d+m/g, '')
@@ -35,7 +33,7 @@ if (!isMainThread) {
 } else {
   t.afterEach(() => loggerSpy.resetHistory())
 
-  t.test('Printing - Default options', (t: Test) => {
+  t.test('Printing - Default options', t => {
     cronometro(
       {
         single() {
@@ -48,7 +46,7 @@ if (!isMainThread) {
           throw new Error('FAILED')
         }
       },
-      (err: Error | null, results: Results) => {
+      (err, results) => {
         t.equal(err, null)
         t.strictSame(Object.keys(results), ['single', 'multiple', 'error'])
 
@@ -89,7 +87,7 @@ if (!isMainThread) {
     )
   })
 
-  t.test('Printing - No colors', (t: Test) => {
+  t.test('Printing - No colors', t => {
     cronometro(
       {
         single() {
@@ -103,7 +101,7 @@ if (!isMainThread) {
         }
       },
       { print: { colors: false } },
-      (err: Error | null) => {
+      err => {
         t.equal(err, null)
 
         const output = loggerSpy.getCall(0).args[0]
@@ -116,7 +114,7 @@ if (!isMainThread) {
     )
   })
 
-  t.test('Printing - Base compare', (t: Test) => {
+  t.test('Printing - Base compare', t => {
     cronometro(
       {
         single() {
@@ -130,7 +128,7 @@ if (!isMainThread) {
         }
       },
       { print: { compare: true } },
-      (err: Error | null) => {
+      err => {
         t.equal(err, null)
 
         const output = removeStyle(loggerSpy.getCall(0).args[0])
@@ -147,7 +145,7 @@ if (!isMainThread) {
     )
   })
 
-  t.test('Printing - Previous compare', (t: Test) => {
+  t.test('Printing - Previous compare', t => {
     cronometro(
       {
         single() {
@@ -161,7 +159,7 @@ if (!isMainThread) {
         }
       },
       { print: { compare: true, compareMode: 'previous' } },
-      (err: Error | null) => {
+      err => {
         t.equal(err, null)
 
         const output = removeStyle(loggerSpy.getCall(0).args[0])
diff --git a/test/success.test.ts b/test/success.test.ts
index 1c0cb75..bf7cac4 100644
--- a/test/success.test.ts
+++ b/test/success.test.ts
@@ -4,8 +4,6 @@ import t from 'tap'
 import { isMainThread } from 'worker_threads'
 import { cronometro, percentiles } from '../src'
 
-type Test = typeof t
-
 if (!isMainThread) {
   cronometro(
     {
@@ -20,7 +18,7 @@ if (!isMainThread) {
     () => false
   )
 } else {
-  t.only('Collecting results', async (t: Test) => {
+  t.only('Collecting results', async t => {
     const results = await cronometro(
       {
         single() {
diff --git a/test/unhandledErrorHandling.test.ts b/test/unhandledErrorHandling.test.ts
index a1198f7..30fb2b3 100644
--- a/test/unhandledErrorHandling.test.ts
+++ b/test/unhandledErrorHandling.test.ts
@@ -4,8 +4,6 @@ import t from 'tap'
 import { isMainThread } from 'worker_threads'
 import { Callback, cronometro, percentiles } from '../src'
 
-type Test = typeof t
-
 if (!isMainThread) {
   cronometro(
     {
@@ -23,7 +21,7 @@ if (!isMainThread) {
     () => false
   )
 } else {
-  t.test('Unhandled errored tests handling', async (t: Test) => {
+  t.test('Unhandled errored tests handling', async t => {
     const results = await cronometro(
       {
         single() {
diff --git a/test/worker.test.ts b/test/worker.test.ts
index f1447b7..f5c7440 100644
--- a/test/worker.test.ts
+++ b/test/worker.test.ts
@@ -5,9 +5,8 @@ import { percentiles, Test } from '../src'
 import { runWorker } from '../src/worker'
 
 const { spy, stub } = sinon
-type TapTest = typeof t
 
-t.test('Worker execution - Handle sync functions that succeed', (t: TapTest) => {
+t.test('Worker execution - Handle sync functions that succeed', t => {
   const main = stub()
   const notifier = spy()
 
@@ -21,7 +20,7 @@ t.test('Worker execution - Handle sync functions that succeed', (t: TapTest) =>
       errorThreshold: 100
     },
     notifier,
-    (code: number) => {
+    code => {
       t.equal(code, 0)
       t.ok(main.called)
 
@@ -45,7 +44,7 @@ t.test('Worker execution - Handle sync functions that succeed', (t: TapTest) =>
   )
 })
 
-t.test('Worker execution - Handle sync functions that throw errors', (t: TapTest) => {
+t.test('Worker execution - Handle sync functions that throw errors', t => {
   const main = stub().throws(new Error('FAILED'))
   const notifier = spy()
 
@@ -59,7 +58,7 @@ t.test('Worker execution - Handle sync functions that throw errors', (t: TapTest
       errorThreshold: 100
     },
     notifier,
-    (code: number) => {
+    code => {
       t.equal(code, 1)
       t.ok(main.called)
 
@@ -81,7 +80,7 @@ t.test('Worker execution - Handle sync functions that throw errors', (t: TapTest
   )
 })
 
-t.test('Worker execution - Handle callback functions that succeed', (t: TapTest) => {
+t.test('Worker execution - Handle callback functions that succeed', t => {
   function main(cb: (err?: Error) => void): void {
     cb()
   }
@@ -100,7 +99,7 @@ t.test('Worker execution - Handle callback functions that succeed', (t: TapTest)
       errorThreshold: 1e-9
     },
     notifier,
-    (code: number) => {
+    code => {
       t.equal(code, 0)
       t.ok(mainSpy.called)
 
@@ -124,7 +123,7 @@ t.test('Worker execution - Handle callback functions that succeed', (t: TapTest)
   )
 })
 
-t.test('Worker execution - Handle callback functions that throw errors', (t: TapTest) => {
+t.test('Worker execution - Handle callback functions that throw errors', t => {
   function main(cb: (err?: Error) => void): void {
     cb(new Error('FAILED'))
   }
@@ -143,7 +142,7 @@ t.test('Worker execution - Handle callback functions that throw errors', (t: Tap
       errorThreshold: 0
     },
     notifier,
-    (code: number) => {
+    code => {
       t.equal(code, 1)
       t.ok(mainSpy.called)
 
@@ -165,7 +164,7 @@ t.test('Worker execution - Handle callback functions that throw errors', (t: Tap
   )
 })
 
-t.test('Worker execution - Handle promise functions that resolve', (t: TapTest) => {
+t.test('Worker execution - Handle promise functions that resolve', t => {
   const main = stub().resolves()
   const notifier = spy()
 
@@ -180,7 +179,7 @@ t.test('Worker execution - Handle promise functions that resolve', (t: TapTest)
       errorThreshold: 0
     },
     notifier,
-    (code: number) => {
+    code => {
       t.equal(code, 0)
       t.ok(main.called)
 
@@ -204,7 +203,7 @@ t.test('Worker execution - Handle promise functions that resolve', (t: TapTest)
   )
 })
 
-t.test('Worker execution - Handle promise functions that reject', (t: TapTest) => {
+t.test('Worker execution - Handle promise functions that reject', t => {
   const main = stub().rejects(new Error('FAILED'))
   const notifier = spy()
 
@@ -219,7 +218,7 @@ t.test('Worker execution - Handle promise functions that reject', (t: TapTest) =
       errorThreshold: 0
     },
     notifier,
-    (code: number) => {
+    code => {
       t.equal(code, 1)
       t.ok(main.called)
 
@@ -241,7 +240,7 @@ t.test('Worker execution - Handle promise functions that reject', (t: TapTest) =
   )
 })
 
-t.test('Worker execution - Handle warmup mode enabled', (t: TapTest) => {
+t.test('Worker execution - Handle warmup mode enabled', t => {
   const main = stub()
   const notifier = spy()
 
@@ -256,7 +255,7 @@ t.test('Worker execution - Handle warmup mode enabled', (t: TapTest) => {
       errorThreshold: 0
     },
     notifier,
-    (code: number) => {
+    code => {
       t.equal(code, 0)
       t.equal(main.callCount, 10)
       t.equal(notifier.callCount, 1)
@@ -281,7 +280,7 @@ t.test('Worker execution - Handle warmup mode enabled', (t: TapTest) => {
   )
 })
 
-t.test('Worker execution - Handle warmup mode disabled', (t: TapTest) => {
+t.test('Worker execution - Handle warmup mode disabled', t => {
   const main = stub()
   const notifier = spy()
 
@@ -296,7 +295,7 @@ t.test('Worker execution - Handle warmup mode disabled', (t: TapTest) => {
       errorThreshold: 0
     },
     notifier,
-    (code: number) => {
+    code => {
       t.equal(code, 0)
       t.equal(main.callCount, 5)
       t.equal(notifier.callCount, 1)
@@ -321,7 +320,7 @@ t.test('Worker execution - Handle warmup mode disabled', (t: TapTest) => {
   )
 })
 
-t.test('Worker setup - Handle callback before functions', (t: TapTest) => {
+t.test('Worker setup - Handle callback before functions', t => {
   const main = stub()
   const setup = spy()
   const notifier = spy()
@@ -347,7 +346,7 @@ t.test('Worker setup - Handle callback before functions', (t: TapTest) => {
       errorThreshold: 100
     },
     notifier,
-    (code: number) => {
+    code => {
       t.equal(code, 0)
       t.equal(setup.callCount, 1)
       t.ok(main.called)
@@ -373,7 +372,7 @@ t.test('Worker setup - Handle callback before functions', (t: TapTest) => {
   )
 })
 
-t.test('Worker setup - Handle callback before functions that throw errors', (t: TapTest) => {
+t.test('Worker setup - Handle callback before functions that throw errors', t => {
   const main = stub()
   const notifier = spy()
 
@@ -397,7 +396,7 @@ t.test('Worker setup - Handle callback before functions that throw errors', (t:
       errorThreshold: 100
     },
     notifier,
-    (code: number) => {
+    code => {
       t.equal(code, 1)
       t.notOk(main.called)
 
@@ -419,7 +418,7 @@ t.test('Worker setup - Handle callback before functions that throw errors', (t:
   )
 })
 
-t.test('Worker setup - Handle promise before functions that resolve', (t: TapTest) => {
+t.test('Worker setup - Handle promise before functions that resolve', t => {
   const main = stub()
   const setup = spy()
   const notifier = spy()
@@ -432,8 +431,9 @@ t.test('Worker setup - Handle promise before functions that resolve', (t: TapTes
           'main',
           {
             test: main,
-            async before(): Promise<void> {
+            before() {
               setup()
+              return Promise.resolve()
             }
           }
         ]
@@ -444,7 +444,7 @@ t.test('Worker setup - Handle promise before functions that resolve', (t: TapTes
       errorThreshold: 100
     },
     notifier,
-    (code: number) => {
+    code => {
       t.equal(code, 0)
       t.equal(setup.callCount, 1)
       t.ok(main.called)
@@ -470,7 +470,7 @@ t.test('Worker setup - Handle promise before functions that resolve', (t: TapTes
   )
 })
 
-t.test('Worker setup - Handle promise before functions that reject', (t: TapTest) => {
+t.test('Worker setup - Handle promise before functions that reject', t => {
   const main = stub()
   const notifier = spy()
 
@@ -482,8 +482,8 @@ t.test('Worker setup - Handle promise before functions that reject', (t: TapTest
           'main',
           {
             test: main,
-            async before(): Promise<void> {
-              throw new Error('FAILED')
+            before() {
+              return Promise.reject(new Error('FAILED'))
             }
           }
         ]
@@ -494,7 +494,7 @@ t.test('Worker setup - Handle promise before functions that reject', (t: TapTest
       errorThreshold: 100
     },
     notifier,
-    (code: number) => {
+    code => {
       t.equal(code, 1)
       t.notOk(main.called)
 
@@ -516,7 +516,7 @@ t.test('Worker setup - Handle promise before functions that reject', (t: TapTest
   )
 })
 
-t.test('Worker setup - Handle callback after functions', (t: TapTest) => {
+t.test('Worker setup - Handle callback after functions', t => {
   const main = stub()
   const setup = spy()
   const notifier = spy()
@@ -542,7 +542,7 @@ t.test('Worker setup - Handle callback after functions', (t: TapTest) => {
       errorThreshold: 100
     },
     notifier,
-    (code: number) => {
+    code => {
       t.equal(code, 0)
       t.equal(setup.callCount, 1)
       t.ok(main.called)
@@ -568,7 +568,7 @@ t.test('Worker setup - Handle callback after functions', (t: TapTest) => {
   )
 })
 
-t.test('Worker setup - Handle callback after functions that throw errors', (t: TapTest) => {
+t.test('Worker setup - Handle callback after functions that throw errors', t => {
   const main = stub()
   const notifier = spy()
 
@@ -592,7 +592,7 @@ t.test('Worker setup - Handle callback after functions that throw errors', (t: T
       errorThreshold: 100
     },
     notifier,
-    (code: number) => {
+    code => {
       t.equal(code, 1)
       t.ok(main.called)
 
@@ -614,7 +614,7 @@ t.test('Worker setup - Handle callback after functions that throw errors', (t: T
   )
 })
 
-t.test('Worker setup - Handle promise after functions that resolve', (t: TapTest) => {
+t.test('Worker setup - Handle promise after functions that resolve', t => {
   const main = stub()
   const setup = spy()
   const notifier = spy()
@@ -627,8 +627,9 @@ t.test('Worker setup - Handle promise after functions that resolve', (t: TapTest
           'main',
           {
             test: main,
-            async after(): Promise<void> {
+            after() {
               setup()
+              return Promise.resolve()
             }
           }
         ]
@@ -639,7 +640,7 @@ t.test('Worker setup - Handle promise after functions that resolve', (t: TapTest
       errorThreshold: 100
     },
     notifier,
-    (code: number) => {
+    code => {
       t.equal(code, 0)
       t.equal(setup.callCount, 1)
       t.ok(main.called)
@@ -665,7 +666,7 @@ t.test('Worker setup - Handle promise after functions that resolve', (t: TapTest
   )
 })
 
-t.test('Worker setup - Handle promise after functions that reject', (t: TapTest) => {
+t.test('Worker setup - Handle promise after functions that reject', t => {
   const main = stub()
   const notifier = spy()
 
@@ -677,8 +678,8 @@ t.test('Worker setup - Handle promise after functions that reject', (t: TapTest)
           'main',
           {
             test: main,
-            async after(): Promise<void> {
-              throw new Error('FAILED')
+            after() {
+              return Promise.reject(new Error('FAILED'))
             }
           }
         ]
@@ -689,7 +690,7 @@ t.test('Worker setup - Handle promise after functions that reject', (t: TapTest)
       errorThreshold: 100
     },
     notifier,
-    (code: number) => {
+    code => {
       t.equal(code, 1)
       t.ok(main.called)
 
@@ -711,7 +712,7 @@ t.test('Worker setup - Handle promise after functions that reject', (t: TapTest)
   )
 })
 
-t.test('Worker execution - Handle empty tests', (t: TapTest) => {
+t.test('Worker execution - Handle empty tests', t => {
   const notifier = spy()
 
   runWorker(
@@ -724,7 +725,7 @@ t.test('Worker execution - Handle empty tests', (t: TapTest) => {
       errorThreshold: 100
     },
     notifier,
-    (code: number) => {
+    code => {
       t.equal(code, 0)
 
       const result = notifier.getCall(0).args[0]