test: add coverage for utility modules (#718)

* test: add coverage for utility modules

Add tests for enforceArray, withExt, lazy, isPlainObject,
deepMerge, and populate — all previously untested pure
utility functions.

* fixup: address review feedback

- Simplify enforceArray tests to two cases (array vs non-array)
- Remove redundant multiple-substitutions test for populate

Author: wilsonwangdev

src/utils/__tests__/array.test.mjs

@@ -0,0 +1,17 @@
+'use strict';
+
+import assert from 'node:assert/strict';
+import { describe, it } from 'node:test';
+
+import { enforceArray } from '../array.mjs';
+
+describe('enforceArray', () => {
+  it('should return the same array if given an array', () => {
+    const input = [1, 2, 3];
+    assert.strictEqual(enforceArray(input), input);
+  });
+
+  it('should wrap a non-array value in an array', () => {
+    assert.deepStrictEqual(enforceArray('hello'), ['hello']);
+  });
+});

src/utils/__tests__/file.test.mjs

@@ -0,0 +1,26 @@
+'use strict';
+
+import assert from 'node:assert/strict';
+import { describe, it } from 'node:test';
+
+import { withExt } from '../file.mjs';
+
+describe('withExt', () => {
+  it('should replace an existing extension', () => {
+    assert.strictEqual(withExt('file.md', 'html'), 'file.html');
+    assert.strictEqual(withExt('path/to/file.md', 'json'), 'path/to/file.json');
+  });
+
+  it('should add an extension when there is none', () => {
+    assert.strictEqual(withExt('file', 'html'), 'file.html');
+  });
+
+  it('should strip the extension when ext is empty', () => {
+    assert.strictEqual(withExt('file.md', ''), 'file');
+    assert.strictEqual(withExt('file.md'), 'file');
+  });
+
+  it('should handle files with multiple dots', () => {
+    assert.strictEqual(withExt('file.test.mjs', 'js'), 'file.test.js');
+  });
+});

src/utils/__tests__/misc.test.mjs

@@ -0,0 +1,56 @@
+'use strict';
+
+import assert from 'node:assert/strict';
+import { describe, it } from 'node:test';
+
+import { lazy, isPlainObject, deepMerge } from '../misc.mjs';
+
+describe('lazy', () => {
+  it('should call the function only once and cache the result', () => {
+    let callCount = 0;
+    const fn = lazy(() => {
+      callCount++;
+      return 42;
+    });
+
+    assert.strictEqual(fn(), 42);
+    assert.strictEqual(fn(), 42);
+    assert.strictEqual(callCount, 1);
+  });
+});
+
+describe('isPlainObject', () => {
+  it('should return true for plain objects', () => {
+    assert.strictEqual(isPlainObject({}), true);
+    assert.strictEqual(isPlainObject({ a: 1 }), true);
+  });
+
+  it('should return false for arrays', () => {
+    assert.strictEqual(isPlainObject([]), false);
+    assert.strictEqual(isPlainObject([1, 2]), false);
+  });
+
+  it('should return false for null and primitives', () => {
+    assert.strictEqual(isPlainObject(null), false);
+    assert.strictEqual(isPlainObject(undefined), false);
+    assert.strictEqual(isPlainObject(42), false);
+    assert.strictEqual(isPlainObject('string'), false);
+  });
+});
+
+describe('deepMerge', () => {
+  it('should merge flat objects with source taking precedence over base', () => {
+    const result = deepMerge({ a: 1, b: 2 }, { b: 10, c: 3 });
+    assert.deepStrictEqual(result, { a: 1, b: 2, c: 3 });
+  });
+
+  it('should merge nested objects recursively', () => {
+    const result = deepMerge({ nested: { a: 1 } }, { nested: { b: 2 } });
+    assert.deepStrictEqual(result, { nested: { a: 1, b: 2 } });
+  });
+
+  it('should use base values when source values are undefined', () => {
+    const result = deepMerge({ a: undefined }, { a: 'base' });
+    assert.deepStrictEqual(result, { a: 'base' });
+  });
+});

src/utils/configuration/__tests__/templates.test.mjs

@@ -0,0 +1,26 @@
+'use strict';
+
+import assert from 'node:assert/strict';
+import { describe, it } from 'node:test';
+
+import { populate } from '../templates.mjs';
+
+describe('populate', () => {
+  it('should substitute template variables from config', () => {
+    const result = populate('https://github.com/{repository}/blob/{ref}/', {
+      repository: 'nodejs/node',
+      ref: 'main',
+    });
+    assert.strictEqual(result, 'https://github.com/nodejs/node/blob/main/');
+  });
+
+  it('should use fallback when config value is missing', () => {
+    const result = populate('{name|unknown}', {});
+    assert.strictEqual(result, 'unknown');
+  });
+
+  it('should leave the placeholder as-is when no value or fallback', () => {
+    const result = populate('{missing}', {});
+    assert.strictEqual(result, '{missing}');
+  });
+});