feat: 🔖 0.4.0 - Add the IsNullable and IsNonNullable types - Check if a type is nullable or not

Author: CRBroughton

CHANGELOG.md

@@ -1,5 +1,11 @@
 # @crbroughton/ts-test-utils
 
+## 0.4.0
+
+### Minor Changes
+
+- Add the IsNullable and IsNonNullable types - Check if a type is nullable or not
+
 ## 0.3.0
 
 ### Minor Changes

README.md

@@ -12,6 +12,8 @@ A collection of helper TypeScript types to test other TypeScript types. This col
 - isNotArray - Checks if a type is not an array
 - Length - Check a given types length; Combine this with the 'Equals' type checker
 - Position - Returns a type in the given position of an array; Combine this with the 'Equals' type checker
+- IsNullable - Check if a type is nullable
+- IsNonNullable - Check if a type is not nullable
 
 ## Installation
 

index.ts

@@ -22,3 +22,7 @@ export type Position<T extends any[], U extends number> =
     T extends [] ? never :
       T extends any[]
         ? T[U] : never
+
+export type IsNullable<T> = null extends T ? true : false
+
+export type IsNonNullable<T> = IsNullable<T> extends true ? false : true

package.json

@@ -1,7 +1,7 @@
 {
   "name": "@crbroughton/ts-test-utils",
   "type": "module",
-  "version": "0.3.0",
+  "version": "0.4.0",
   "description": "A collection of testing helper types",
   "author": "Craig R Broughton",
   "license": "MIT",

tests/IsNonNullable.test.ts

@@ -0,0 +1,15 @@
+/* eslint-disable unused-imports/no-unused-vars */
+import { describe, it } from 'bun:test'
+import type { Expect, IsNonNullable } from '../index'
+
+describe('IsNonNulable tests', () => {
+  it('Passes the IsNonNulable test when the type is not nullable', () => {
+    type Result = Expect<IsNonNullable<{ id: number }>>
+    //   ^?
+  })
+  it('Failed the IsNonNulable test when the type is nullable', () => {
+    // @ts-expect-error - Fails the IsNonNulable test
+    type Result = Expect<IsNonNullable<{ id: string } | null>>
+    //   ^?
+  })
+})

tests/IsNullable.test.ts

@@ -0,0 +1,15 @@
+/* eslint-disable unused-imports/no-unused-vars */
+import { describe, it } from 'bun:test'
+import type { Expect, IsNullable } from '../index'
+
+describe('IsNullable tests', () => {
+  it('Passes the IsNullable test when the type is nullable', () => {
+    type Result = Expect<IsNullable<{ id: number } | null>>
+    //   ^?
+  })
+  it('Failed the IsNullable test when the type is not nullable', () => {
+    // @ts-expect-error - Fails the exclusion
+    type Result = Expect<IsNullable<{ id: string }>>
+    //   ^?
+  })
+})