feat: add toBeSnakeCase

src/Mixins/Expectation.php

@@ -1009,4 +1009,16 @@ final class Expectation
 
         return $this;
     }
+
+    /**
+     * Asserts that the value is snake_case.
+     *
+     * @return self<TValue>
+     */
+    public function toBeSnakeCase(string $message = ''): self
+    {
+        Assert::assertTrue((bool) preg_match('/^[\p{Ll}_]+$/u', (string) $this->value), $message);
+
+        return $this;
+    }
 }

tests/Features/Expect/toBeSnakeCase.php

@@ -0,0 +1,23 @@
+<?php
+
+use PHPUnit\Framework\ExpectationFailedException;
+
+test('pass', function () {
+    expect('abc')->toBeSnakeCase();
+    expect('abc_def')->toBeSnakeCase();
+    expect('abc-def')->not->toBeSnakeCase();
+    expect('abcDef')->not->toBeSnakeCase();
+    expect('AbcDef')->not->toBeSnakeCase();
+});
+
+test('failures', function () {
+    expect('Abc')->toBeSnakeCase();
+})->throws(ExpectationFailedException::class);
+
+test('failures with custom message', function () {
+    expect('Abc')->toBeSnakeCase('oh no!');
+})->throws(ExpectationFailedException::class, 'oh no!');
+
+test('not failures', function () {
+    expect('abc_def')->not->toBeSnakeCase();
+})->throws(ExpectationFailedException::class);