diff --git a/typescript/option/src/helpers/flat.test.ts b/typescript/option/src/helpers/flat.test.ts
new file mode 100644
index 0000000..2f52ec2
--- /dev/null
+++ b/typescript/option/src/helpers/flat.test.ts
@@ -0,0 +1,25 @@
+import { expect } from 'chai'
+import { flat } from './flat'
+import { None, Some } from '../types'
+import { someX } from '../../test/constants'
+
+describe('The flat helper', () => {
+    it('should return None when given None', () => {
+        // act
+        const result = flat(None)
+
+        // assert
+        expect(result).to.equal(None)
+    })
+
+    it('should return the inner Some(x) when given Some(Some(x))', () => {
+        // arrange
+        const value = Some(someX)
+
+        // act
+        const result = flat(value)
+
+        // assert
+        expect(result).to.equal(someX)
+    })
+})