feat(packages/stdlib): add first arrays util

packages/stdlib/src/arrays/first/index.test.ts

@@ -0,0 +1,23 @@
+import { describe, it, expect } from 'vitest';
+import { first } from '.';
+
+describe('first', () => {
+  it('return the first element of a non-empty array', () => {
+    expect(first([1, 2, 3])).toBe(1);
+    expect(first(['a', 'b', 'c'])).toBe('a');
+  });
+
+  it('return undefined for an empty array without a default value', () => {
+    expect(first([])).toBeUndefined();
+  });
+
+  it('return the default value for an empty array with a default value', () => {
+    expect(first([], 42)).toBe(42);
+    expect(first([], 'default')).toBe('default');
+  });
+
+  it('return the first element even if a default value is provided', () => {
+    expect(first([1, 2, 3], 42)).toBe(1);
+    expect(first(['a', 'b', 'c'], 'default')).toBe('a');
+  });
+});