Add some tests + phpdoc

tests/FitsHeaderTest.php

@@ -0,0 +1,24 @@
+<?php
+
+declare(strict_types=1);
+
+use PHPUnit\Framework\TestCase;
+
+final class FitsHeaderTest extends TestCase
+{
+    public function testKeywordValue(): void
+    {
+        $fits = new Dumbastro\FitsPhp\Fits(__DIR__ . '/test_orion.fit');
+        $header = new Dumbastro\FitsPhp\FitsHeader($fits->headerBlock);
+
+        $this->assertSame(
+            trim($header->getKeywordValue('BITPIX')),
+            '16'
+        );
+        $this->assertSame(
+            trim($header->getKeywordValue('NAXIS')),
+            '3'
+        );
+    }
+}
+ 

tests/FitsTest.php

@@ -0,0 +1,16 @@
+<?php
+
+declare(strict_types=1);
+
+use PHPUnit\Framework\TestCase;
+
+final class FitsTest extends TestCase
+{
+    public function testValidatesFits(): void
+    {
+        $fits = new Dumbastro\FitsPhp\Fits(__DIR__ . '/test_orion.fit');
+
+        $this->assertTrue($fits->validate());
+    }
+}
+