test: Implement unit tests for this project

There are two spec files, `lsfnd.spec.cjs` for CommonJS test, and `lsfnd.spec.mjs` for ES Modules test. Additionally, added NPM scripts to run the tests.

package.json

@@ -22,7 +22,10 @@
     "build": "ts-node scripts/build.ts",
     "minify": "ts-node scripts/build.ts --minify",
     "docs": "npm run-script build:docs",
-    "build:docs": "typedoc --options typedoc.config.js"
+    "build:docs": "typedoc --options typedoc.config.js",
+    "test": "node test/lsfnd.spec.cjs && node test/lsfnd.spec.mjs",
+    "test:cjs": "node test/lsfnd.spec.cjs",
+    "test:mjs": "node test/lsfnd.spec.mjs"
   },
   "repository": {
     "type": "git",

test/lsfnd.spec.cjs

@@ -0,0 +1,29 @@
+const { join, basename } = require('node:path');
+const { ls, lsFiles, lsDirs } = require('..');
+const { it, rejects, deepEq } = require('./lib/simpletest');
+
+console.log(`\n\x1b[1m${basename(__filename)}:\x1b[0m`);
+
+it('test `ls` function by listing this file directory', async () => {
+  const results = await ls(__dirname, {}, 0);
+  const expected = [ 'lib', 'lsfnd.spec.cjs', 'lsfnd.spec.mjs' ]
+    .map((e) => join(__dirname, e));
+  deepEq(results, expected);
+}, false);
+
+it('test `lsFiles` function by listing this file directory', async () => {
+  const results = await lsFiles(__dirname);
+  const expected = [ 'lsfnd.spec.cjs', 'lsfnd.spec.mjs' ]
+    .map((e) => join(__dirname, e));
+  deepEq(results, expected);
+}, false);
+
+it('test `lsDirs` function by listing this file directory', async () => {
+  const results = await lsDirs(__dirname);
+  const expected = [ 'lib' ].map((e) => join(__dirname, e));
+  deepEq(results, expected);
+}, false);
+
+it('throws an error if given directory path not exist', async () => {
+  await rejects(ls('./this/is/not/exist/directory/path'), Error);
+}, false);

test/lsfnd.spec.mjs

@@ -0,0 +1,35 @@
+import { join, dirname, basename } from 'node:path';
+import { fileURLToPath } from 'node:url';
+import { ls, lsFiles, lsDirs } from '../dist/index.js';
+import test from './lib/simpletest.js';
+const { it, rejects, deepEq } = test;
+
+// Create the '__dirname' and '__filename' variable, because in ESM these are not defined
+const __filename = fileURLToPath(import.meta.url);
+const __dirname = dirname(__filename);
+
+console.log(`\n\x1b[1m${basename(__filename)}:\x1b[0m`);
+
+it('test `ls` function by listing this file directory', async () => {
+  const results = await ls(__dirname, {}, 0);
+  const expected = [ 'lib', 'lsfnd.spec.cjs', 'lsfnd.spec.mjs' ]
+    .map((e) => join(__dirname, e));
+  deepEq(results, expected);
+}, false);
+
+it('test `lsFiles` function by listing this file directory', async () => {
+  const results = await lsFiles(__dirname);
+  const expected = [ 'lsfnd.spec.cjs', 'lsfnd.spec.mjs' ]
+    .map((e) => join(__dirname, e));
+  deepEq(results, expected);
+}, false);
+
+it('test `lsDirs` function by listing this file directory', async () => {
+  const results = await lsDirs(__dirname);
+  const expected = [ 'lib' ].map((e) => join(__dirname, e));
+  deepEq(results, expected);
+}, false);
+
+it('throws an error if given directory path not exist', async () => {
+  await rejects(ls('./this/is/not/exist/directory/path'), Error);
+}, false);