diff --git a/test/main.js b/test/main.js
new file mode 100644
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+++ b/test/main.js
@@ -0,0 +1,78 @@
+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.asMinute(), 60 * 24 * 365.25 / 2)
+            a.strictEqual(d.asHour(), 24 * 365.25 / 2)
+            a.strictEqual(d.asDay(), 365.25 / 2)
+            a.strictEqual(d.asWeek(), 365.25 / 7 / 2)
+            a.strictEqual(d.asYear(), .5)
+        })
+
+        it('add / subtract', () => {
+            const d = new Duration(1, 'day')
+            d.add(4, 'hours')
+            a.strictEqual(d.asHour(), 28)
+            d.subtract(.5, 'day')
+            a.strictEqual(d.asHour(), 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`)
+        })
+    })
+
+})
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