Tests for marshalHeadersFromSapi function

- integer keys should be ignored
- `_` should be changed to `-` in key (also for `CONTENT_*` headers)

Author: michalbundyra

test/functions/MarshalHeadersFromSapiTest.php

@@ -0,0 +1,66 @@
+<?php
+/**
+ * @see       https://github.com/zendframework/zend-diactoros for the canonical source repository
+ * @copyright Copyright (c) 2019 Zend Technologies USA Inc. (https://www.zend.com)
+ * @license   https://github.com/zendframework/zend-diactoros/blob/master/LICENSE.md New BSD License
+ */
+
+declare(strict_types=1);
+
+namespace ZendTest\Diactoros\functions;
+
+use PHPUnit\Framework\TestCase;
+
+use function Zend\Diactoros\marshalHeadersFromSapi;
+
+class MarshalHeadersFromSapiTest extends TestCase
+{
+    public function testReturnsHeaders() : void
+    {
+        $server = [
+            'REDIRECT_CONTENT_FOO' => 'redirect-foo',
+            'CONTENT_FOO' => null,
+            'REDIRECT_CONTENT_BAR' => 'redirect-bar',
+            'CONTENT_BAR' => '',
+            'REDIRECT_CONTENT_BAZ' => 'redirect-baz',
+            'CONTENT_BAZ' => 'baz',
+            'REDIRECT_CONTENT_VAR' => 'redirect-var',
+
+            'REDIRECT_HTTP_ABC' => 'redirect-abc',
+            'HTTP_ABC' => null,
+            'REDIRECT_HTTP_DEF' => 'redirect-def',
+            'HTTP_DEF' => '',
+            'REDIRECT_HTTP_GHI' => 'redirect-ghi',
+            'HTTP_GHI' => 'ghi',
+            'REDIRECT_HTTP_JKL' => 'redirect-jkl',
+
+            'HTTP_TEST_MNO' => 'mno',
+            'HTTP_TEST_PQR' => '',
+            'HTTP_TEST_STU' => null,
+            'CONTENT_TEST_VW' => 'vw',
+            'CONTENT_TEST_XY' => '',
+            'CONTENT_TEST_ZZ' => null,
+
+            123 => 'integer',
+        ];
+
+        $expectedHeaders = [
+            'content-foo' => null,
+            'content-baz' => 'baz',
+            'content-var' => 'redirect-var',
+
+            'abc' => null,
+            'ghi' => 'ghi',
+            'jkl' => 'redirect-jkl',
+
+            'test-mno' => 'mno',
+            'test-stu' => null,
+            'content-test-vw' => 'vw',
+            'content-test-zz' => null,
+        ];
+
+        $headers = marshalHeadersFromSapi($server);
+
+        self::assertSame($expectedHeaders, $headers);
+    }
+}