typescript(option): test: wrote tests for the 'withDefault' helper

Signed-off-by: prescientmoon <git@moonythm.dev>

typescript/option/src/helpers/withDefault.test.ts

@@ -0,0 +1,22 @@
+import { expect } from 'chai'
+import { withDefault } from './withDefault'
+import { x } from '../../test/constants'
+import { None, Some } from '../types'
+
+describe('The withDefault helper', () => {
+    it('should return the default when given None', () => {
+        // act
+        const result = withDefault(x, None)
+
+        // assert
+        expect(result).to.equal(x)
+    })
+
+    it('should return x when given Some(x)', () => {
+        // act
+        const result = withDefault(0, Some(1))
+
+        // assert
+        expect(result).to.equal(1)
+    })
+})