fix: validate icons to be images (#1167)

tests/Unit/helpers/IsImageTest.php

@@ -0,0 +1,42 @@
+<?php
+
+namespace Tests\Unit\helpers;
+
+use Tests\TestCase;
+
+class IsImageTest extends TestCase
+{
+    /**
+     * @return void
+     */
+    public function test_isImage_returns_false_when_file_is_not_image()
+    {
+        $actual = isImage("<?php ?>");
+
+        $this->assertFalse($actual);
+    }
+
+    /**
+     * @return void
+     */
+    public function test_isImage_returns_true_when_file_is_image()
+    {
+        $file = file_get_contents(__DIR__ . '/fixtures/heimdall-icon-small.png');
+
+        $actual = isImage($file);
+
+        $this->assertTrue($actual);
+    }
+
+    /**
+     * @return void
+     */
+    public function test_isImage_returns_false_when_file_is_php_but_png()
+    {
+        $file = file_get_contents(__DIR__ . '/fixtures/heimdall-icon-small-php.php');
+
+        $actual = isImage($file);
+
+        $this->assertTrue($actual);
+    }
+}