Schema\TypeFormats\StringDate: fix check + add tests

src/Schema/TypeFormats/StringDate.php

@@ -15,6 +15,11 @@ public function __invoke($value): bool
     {
         // full-date notation as defined by RFC 3339, section 5.6, for example, 2017-07-21
 
-        return DateTime::createFromFormat('Y-m-d', $value) !== false;
+        $datetime = DateTime::createFromFormat('Y-m-d', $value);
+        if ($datetime === false) {
+            return false;
+        }
+
+        return $datetime->format('Y-m-d') == $value;
     }
 }

tests/Schema/TypeFormats/StringDateTest.php

@@ -0,0 +1,54 @@
+<?php
+
+declare(strict_types=1);
+
+namespace League\OpenAPIValidation\Tests\Schema\TypeFormats;
+
+use League\OpenAPIValidation\Schema\TypeFormats\StringDate;
+use PHPUnit\Framework\TestCase;
+
+final class StringDateTest extends TestCase
+{
+    /**
+     * @dataProvider dateGreenDataProvider
+     */
+    public function testGreendateTypeFormat(string $date): void
+    {
+        $this->assertTrue((new StringDate())($date));
+    }
+
+    /**
+     * @return string[][]
+     */
+    public function dateGreenDataProvider(): array
+    {
+        return [
+            ['1985-04-12'],
+            ['1937-01-01'],
+            ['1996-12-19'],
+            ['1990-12-31'],
+        ];
+    }
+
+    /**
+     * @dataProvider dateRedDataProvider
+     */
+    public function testRedDateTypeFormat(string $date): void
+    {
+        $this->assertFalse((new StringDate())($date));
+    }
+
+    /**
+     * @return string[][]
+     */
+    public function dateRedDataProvider(): array
+    {
+        return [
+            ['2021-0-32'],
+            ['2021-09-32'],
+            ['0000-00-00'],
+            [''],
+            ['somestring'],
+        ];
+    }
+}