test: core string utils

jest.config.js

@@ -10,5 +10,5 @@ export default {
 		'^(\\.{1,2}/.*)\\.js$': '$1',
 	},
 	testRegex: ['__tests__/.+(spec|test).ts'],
-	setupFiles: ['<rootDir>/packages/core/__tests__/setup.ts'],
+	setupFiles: ['<rootDir>/packages/core/__tests__/setup-tests.ts'],
 };

packages/core/__tests__/setup-tests.ts

@@ -0,0 +1,8 @@
+/**
+ * `wrap-ansi` is an ES Module, and `jest` does not fully support it.
+ *
+ * Related Jest Issue:
+ * 	title: Meta: Native support for ES Modules #9430
+ * 	url: https://github.com/jestjs/jest/issues/9430
+ **/
+jest.mock('wrap-ansi', () => (str: string) => str);

packages/core/__tests__/utils/string.spec.ts

@@ -0,0 +1,18 @@
+import { diffLines } from '../../src/utils';
+
+describe('String Utils', () => {
+	it('should return `undefined` if there is no diff line', () => {
+		const input = 'Lorem Ipsum is simply dummy text\n of the printing \nand typesetting industry.';
+
+		expect(diffLines(input, input)).toBeUndefined();
+	});
+
+	it('should return a list with the index of each diff line', () => {
+		const inputA =
+			'Lorem Ipsum is simply dummy\n text\n of the \nprinting\n \nand typesetting industry.';
+		const inputB =
+			'Lorem Ipsum is simply dummy\n \ntext of the \nprinting\n and\n typesetting industry.';
+
+		expect(diffLines(inputA, inputB)).toStrictEqual([1, 2, 4, 5]);
+	});
+});