diff --git a/package.json b/package.json
index ee28edd..d5234a2 100644
--- a/package.json
+++ b/package.json
@@ -8,7 +8,7 @@
   "scripts": {
     "build": "tsup src/index.ts --format cjs,esm --dts --sourcemap",
     "test": "pnpm run build && mocha",
-    "prepublishOnly": "pnpm run test && pnpm run build"
+    "prepublishOnly": "pnpm run test"
   },
   "main": "./dist/index.cjs",
   "types": "./dist/index.d.ts",
diff --git a/test/main.js b/test/main.js
deleted file mode 100644
index 34bde41..0000000
--- a/test/main.js
+++ /dev/null
@@ -1,78 +0,0 @@
-const { describe, it } = require('mocha')
-const a = require('assert')
-
-const { Duration } = require('../')
-
-describe('Duration', () => {
-
-    describe('Basics', () => {
-
-        it('as unit', () => {
-            const d = new Duration(.5, 'year')
-
-            a.strictEqual(d.asMilliseconds(), 1000 * 60 * 60 * 24 * 365.25 / 2)
-            a.strictEqual(d.asSeconds(), 60 * 60 * 24 * 365.25 / 2)
-            a.strictEqual(d.asMinutes(), 60 * 24 * 365.25 / 2)
-            a.strictEqual(d.asHours(), 24 * 365.25 / 2)
-            a.strictEqual(d.asDays(), 365.25 / 2)
-            a.strictEqual(d.asWeeks(), 365.25 / 7 / 2)
-            a.strictEqual(d.asYears(), .5)
-        })
-
-        it('add / subtract', () => {
-            const d = new Duration(1, 'day')
-            d.add(4, 'hours')
-            a.strictEqual(d.asHours(), 28)
-            d.subtract(.5, 'day')
-            a.strictEqual(d.asHours(), 16)
-        })
-
-        it('exact units', () => {
-            const d = new Duration(1, 'day')
-
-            d.add(42, 'milliseconds')
-            a.strictEqual(d.milliseconds(), 42)
-
-            d.add(5, 'seconds')
-            a.strictEqual(d.seconds(), 5)
-
-            d.add(27, 'minutes')
-            a.strictEqual(d.minutes(), 27)
-
-            d.add(8, 'hours')
-            a.strictEqual(d.hours(), 8)
-
-            d.add(3, 'days')
-            a.strictEqual(d.days(), 4)
-
-            d.add(17, 'weeks')
-            a.strictEqual(d.weeks(), 17)
-
-            d.add(2, 'years')
-            a.strictEqual(d.years(), 2)
-        })
-
-    })
-
-    describe('Humanize', () => {
-
-        it('few minutes', () => {
-            a.strictEqual(new Duration(2, 'minutes').humanize(), 'a few minutes')
-            a.strictEqual(new Duration(16, 'minutes').humanize(), '16 minutes')
-            a.strictEqual(new Duration(30, 'seconds').humanize(), 'a moment')
-        })
-
-        it('custom humanizer', () => {
-            const humanizer = [
-                [d => d.days() > 0, d => `yus for ${d.days()}`],
-                [() => true, () => 'cool'],
-            ]
-
-            const d = new Duration(5, 'minutes')
-            a.strictEqual(d.humanize(humanizer), 'cool')
-            d.add(2, 'days')
-            a.strictEqual(d.humanize(humanizer), `yus for 2`)
-        })
-    })
-
-})
\ No newline at end of file
diff --git a/test/main.mjs b/test/main.mjs
new file mode 100644
index 0000000..cd60b92
--- /dev/null
+++ b/test/main.mjs
@@ -0,0 +1,73 @@
+import { strictEqual } from 'assert'
+import { describe, it } from 'mocha'
+
+import { Duration } from '../dist/index.js'
+
+describe('Duration', () => {
+  describe('Basics', () => {
+    it('as unit', () => {
+      const d = new Duration(0.5, 'year')
+
+      strictEqual(d.asMilliseconds(), (1000 * 60 * 60 * 24 * 365.25) / 2)
+      strictEqual(d.asSeconds(), (60 * 60 * 24 * 365.25) / 2)
+      strictEqual(d.asMinutes(), (60 * 24 * 365.25) / 2)
+      strictEqual(d.asHours(), (24 * 365.25) / 2)
+      strictEqual(d.asDays(), 365.25 / 2)
+      strictEqual(d.asWeeks(), 365.25 / 7 / 2)
+      strictEqual(d.asYears(), 0.5)
+    })
+
+    it('add / subtract', () => {
+      const d = new Duration(1, 'day')
+      d.add(4, 'hours')
+      strictEqual(d.asHours(), 28)
+      d.subtract(0.5, 'day')
+      strictEqual(d.asHours(), 16)
+    })
+
+    it('exact units', () => {
+      const d = new Duration(1, 'day')
+
+      d.add(42, 'milliseconds')
+      strictEqual(d.milliseconds(), 42)
+
+      d.add(5, 'seconds')
+      strictEqual(d.seconds(), 5)
+
+      d.add(27, 'minutes')
+      strictEqual(d.minutes(), 27)
+
+      d.add(8, 'hours')
+      strictEqual(d.hours(), 8)
+
+      d.add(3, 'days')
+      strictEqual(d.days(), 4)
+
+      d.add(17, 'weeks')
+      strictEqual(d.weeks(), 17)
+
+      d.add(2, 'years')
+      strictEqual(d.years(), 2)
+    })
+  })
+
+  describe('Humanize', () => {
+    it('few minutes', () => {
+      strictEqual(new Duration(2, 'minutes').humanize(), 'a few minutes')
+      strictEqual(new Duration(16, 'minutes').humanize(), '16 minutes')
+      strictEqual(new Duration(30, 'seconds').humanize(), 'a moment')
+    })
+
+    it('custom humanizer', () => {
+      const humanizer = [
+        [(d) => d.days() > 0, (d) => `yus for ${d.days()}`],
+        [() => true, () => 'cool'],
+      ]
+
+      const d = new Duration(5, 'minutes')
+      strictEqual(d.humanize(humanizer), 'cool')
+      d.add(2, 'days')
+      strictEqual(d.humanize(humanizer), `yus for 2`)
+    })
+  })
+})