Added some missing tests for Headers class

Author: mnavarrocarter

composer.json

@@ -31,7 +31,7 @@
         "lint": "php-cs-fixer fix",
         "pr": [
             "php-cs-fixer fix --dry-run -vvv",
-            "psalm --stats",
+            "psalm --no-cache --stats",
             "phpunit --testdox --coverage-text"
         ]
     },

tests/HeadersTest.php

@@ -0,0 +1,44 @@
+<?php
+
+namespace MNC\Http;
+
+use PHPUnit\Framework\TestCase;
+
+/**
+ * Class HeadersTest
+ * @package MNC\Http
+ */
+class HeadersTest extends TestCase
+{
+    public function testItConvertsToArrayProperly(): void
+    {
+        $headers = Headers::fromMap([
+            'Content-Type' => 'application/json',
+            'Content-Length' => '3532',
+            'Server' => 'nginx'
+        ]);
+
+        $lines = $headers->toArray();
+
+        self::assertSame('content-type: application/json', $lines[0]);
+        self::assertSame('content-length: 3532', $lines[1]);
+        self::assertSame('server: nginx', $lines[2]);
+        self::assertCount(3, $lines);
+    }
+
+    public function testFilter(): void
+    {
+        $headers = Headers::fromMap([
+            'Content-Type' => 'application/json',
+            'Content-Length' => '3532',
+            'Server' => 'nginx'
+        ]);
+
+        $headers = $headers->filter(fn($value, $name) => $name !== 'server');
+
+        self::assertCount(2, $headers);
+        self::assertArrayHasKey('content-type', $headers);
+        self::assertArrayHasKey('content-length', $headers);
+        self::assertArrayNotHasKey('server', $headers);
+    }
+}