Feature: add boolean rule

src/Rules/Boolean.php

@@ -0,0 +1,63 @@
+<?php
+
+namespace StellarWP\Validation\Rules;
+
+use Closure;
+use StellarWP\Validation\Contracts\Sanitizer;
+use StellarWP\Validation\Contracts\ValidatesOnFrontEnd;
+use StellarWP\Validation\Contracts\ValidationRule;
+
+class Boolean implements ValidationRule, ValidatesOnFrontEnd, Sanitizer
+{
+    /**
+     * {@inheritDoc}
+     *
+     * @unreleased
+     */
+    public static function id(): string
+    {
+        return 'boolean';
+    }
+
+    /**
+     * {@inheritDoc}
+     *
+     * @unreleased
+     */
+    public static function fromString(string $options = null): ValidationRule
+    {
+        return new self();
+    }
+
+    /**
+     * {@inheritDoc}
+     *
+     * @unreleased
+     */
+    public function __invoke($value, Closure $fail, string $key, array $values)
+    {
+        if (!filter_var($value, FILTER_VALIDATE_BOOLEAN)) {
+            $fail(sprintf(__('%s must be an boolean', '%TEXTDOMAIN%'), '{field}'));
+        }
+    }
+
+    /**
+     * {@inheritDoc}
+     *
+     * @unreleased
+     */
+    public function serializeOption()
+    {
+        return null;
+    }
+
+    /**
+     * {@inheritDoc}
+     *
+     * @unreleased
+     */
+    public function sanitize($value)
+    {
+        return filter_var($value, FILTER_VALIDATE_BOOLEAN);
+    }
+}

src/ServiceProvider.php

@@ -4,6 +4,7 @@
 
 namespace StellarWP\Validation;
 
+use StellarWP\Validation\Rules\Boolean;
 use StellarWP\Validation\Rules\Currency;
 use StellarWP\Validation\Rules\DateTime;
 use StellarWP\Validation\Rules\Email;
@@ -48,6 +49,7 @@ class ServiceProvider
         OptionalIf::class,
         OptionalUnless::class,
         DateTime::class,
+        Boolean::class,
     ];
 
     /**

tests/unit/Rules/BooleanTest.php

@@ -0,0 +1,60 @@
+<?php
+
+namespace unit\Rules;
+
+use StellarWP\Validation\Rules\Boolean;
+use StellarWP\Validation\Tests\TestCase;
+
+class BooleanTest extends TestCase
+{
+    /**
+     * @unreleased
+     *
+     * @dataProvider booleansProvider
+     */
+    public function testRuleValidatesBooleans($value, $pass)
+    {
+        $rule = new Boolean();
+
+        if ($pass) {
+            self::assertValidationRulePassed($rule, $value);
+        } else {
+            self::assertValidationRuleFailed($rule, $value);
+        }
+    }
+
+    /**
+     * @unreleased
+     */
+    public function booleansProvider(): array
+    {
+        return [
+            // values that pass
+            [true, true],
+            [1, true],
+            ['1', true],
+            ['true', true],
+            ['yes', true],
+            ['on', true],
+
+            // values that fail
+            [false, false],
+            [0, false],
+            ['0', false],
+            ['false', false],
+            ['no', false],
+            ['off', false],
+            ['abc', false],
+        ];
+    }
+
+    /**
+     * @unreleased
+     */
+    public function testCastsToBoolean()
+    {
+        $rule = new Boolean();
+        self::assertSame(true, $rule->sanitize('1'));
+        self::assertSame(false, $rule->sanitize('0'));
+    }
+}