typescript(option): test: added tests for exists

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

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

@@ -0,0 +1,33 @@
+import { expect } from 'chai'
+import { exists } from './exists'
+import { constantly } from '@thi.ng/compose'
+import { None, Some } from '../types'
+import { x } from '../../test/constants'
+
+describe('The exists helper', () => {
+    it('should return false when given None', () => {
+        // act
+        const result = exists(constantly(true), None)
+
+        // assert
+        expect(result).to.equal(false)
+    })
+
+    describe('When given Some', () => {
+        it('should return true if the callback returns true', () => {
+            // act
+            const result = exists(constantly(true), Some(x))
+
+            // assert
+            expect(result).to.equal(true)
+        })
+
+        it('should return false if the callback returns false', () => {
+            // act
+            const result = exists(constantly(false), Some(x))
+
+            // assert
+            expect(result).to.equal(false)
+        })
+    })
+})