add startswith validation

src/Validation/Rules/StartsWith.php

@@ -0,0 +1,31 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tempest\Validation\Rules;
+
+use Attribute;
+use Tempest\Interface\Rule;
+
+#[Attribute]
+final readonly class StartsWith implements Rule
+{
+    public function __construct(
+        private string $needle,
+    ) {
+    }
+
+    public function isValid(mixed $value): bool
+    {
+        if (str_starts_with($value, $this->needle)) {
+            return true;
+        }
+
+        return false;
+    }
+
+    public function message(): string
+    {
+        return "Value should start with {$this->needle}";
+    }
+}

tests/Validation/Rules/StartsWithTest.php

@@ -0,0 +1,22 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tests\Tempest\Validation\Rules;
+
+use PHPUnit\Framework\TestCase;
+use Tempest\Validation\Rules\StartsWith;
+
+class StartsWithTest extends TestCase
+{
+    /** @test */
+    public function test_starts_with()
+    {
+        $rule = new StartsWith(needle: 'ab');
+
+        $this->assertTrue($rule->isValid('ab'));
+        $this->assertTrue($rule->isValid('abc'));
+        $this->assertFalse($rule->isValid('a'));
+        $this->assertFalse($rule->isValid('3434'));
+    }
+}