diff --git a/src/Renderer/HtmlEngine.php b/src/Renderer/HtmlEngine.php
index 4a48e1f0..75343bbd 100644
--- a/src/Renderer/HtmlEngine.php
+++ b/src/Renderer/HtmlEngine.php
@@ -29,6 +29,6 @@ class HtmlEngine implements EngineInterface
      */
     public function canRender($path)
     {
-        return strpos($path, '.html') && file_exists($path);
+        return strpos($path, '.htm') && file_exists($path);
     }
 }
diff --git a/src/Renderer/Renderer.php b/src/Renderer/Renderer.php
index 5ed7cf31..de31ca74 100644
--- a/src/Renderer/Renderer.php
+++ b/src/Renderer/Renderer.php
@@ -2,8 +2,12 @@
 
 namespace Engelsystem\Renderer;
 
+use Psr\Log\LoggerAwareTrait;
+
 class Renderer
 {
+    use LoggerAwareTrait;
+
     /** @var EngineInterface[] */
     protected $renderer = [];
 
@@ -24,7 +28,10 @@ class Renderer
             return $renderer->get($template, $data);
         }
 
-        engelsystem_error('Unable to find a renderer for template file "' . $template . '".');
+        if ($this->logger) {
+            $this->logger->error('Unable to find a renderer for template file "{file}"', ['file' => $template]);
+        }
+
         return '';
     }
 
diff --git a/tests/Unit/Renderer/HtmlEngineTest.php b/tests/Unit/Renderer/HtmlEngineTest.php
new file mode 100644
index 00000000..0b317b72
--- /dev/null
+++ b/tests/Unit/Renderer/HtmlEngineTest.php
@@ -0,0 +1,67 @@
+<?php
+
+namespace Engelsystem\Test\Config;
+
+use Engelsystem\Renderer\HtmlEngine;
+use PHPUnit\Framework\TestCase;
+
+class HtmlEngineTest extends TestCase
+{
+    /** @var string[] */
+    protected $tmpFileNames = [];
+
+    /**
+     * @covers \Engelsystem\Renderer\HtmlEngine::get
+     */
+    public function testGet()
+    {
+        $engine = new HtmlEngine();
+
+        $file = $this->createTempFile('<div>%main_content%</div>');
+
+        $data = $engine->get($file, ['main_content' => 'Lorem ipsum dolor sit']);
+        $this->assertEquals('<div>Lorem ipsum dolor sit</div>', $data);
+    }
+
+    /**
+     * @covers \Engelsystem\Renderer\HtmlEngine::canRender
+     */
+    public function testCanRender()
+    {
+        $engine = new HtmlEngine();
+
+        $this->assertFalse($engine->canRender('/dev/null'));
+
+        $file = $this->createTempFile();
+        $this->assertTrue($engine->canRender($file));
+
+        $htmFile = $this->createTempFile('', '.htm');
+        $this->assertTrue($engine->canRender($htmFile));
+    }
+
+    /**
+     * @param string $content
+     * @param string $extension
+     * @return string
+     */
+    protected function createTempFile($content = '', $extension = '.html')
+    {
+        $tmpFileName = tempnam(sys_get_temp_dir(), 'EngelsystemUnitTest');
+
+        $fileName = $tmpFileName . $extension;
+        rename($tmpFileName, $fileName);
+
+        file_put_contents($fileName, $content);
+
+        $this->tmpFileNames[] = $fileName;
+
+        return $fileName;
+    }
+
+    public function tearDown()
+    {
+        foreach ($this->tmpFileNames as $fileName) {
+            unlink($fileName);
+        }
+    }
+}
diff --git a/tests/Unit/Renderer/RendererTest.php b/tests/Unit/Renderer/RendererTest.php
new file mode 100644
index 00000000..b0238078
--- /dev/null
+++ b/tests/Unit/Renderer/RendererTest.php
@@ -0,0 +1,55 @@
+<?php
+
+namespace Engelsystem\Test\Config;
+
+use Engelsystem\Renderer\EngineInterface;
+use Engelsystem\Renderer\Renderer;
+use PHPUnit\Framework\TestCase;
+use Psr\Log\LoggerInterface;
+
+class RendererTest extends TestCase
+{
+    public function testGet()
+    {
+        $renderer = new Renderer();
+
+        $nullRenderer = $this->getMockForAbstractClass(EngineInterface::class);
+
+        $nullRenderer->expects($this->atLeastOnce())
+            ->method('canRender')
+            ->willReturn(false);
+        $renderer->addRenderer($nullRenderer);
+
+        $mockRenderer = $this->getMockForAbstractClass(EngineInterface::class);
+
+        $mockRenderer->expects($this->atLeastOnce())
+            ->method('canRender')
+            ->with('foo.template')
+            ->willReturn(true);
+
+        $mockRenderer->expects($this->atLeastOnce())
+            ->method('get')
+            ->with('foo.template', ['lorem' => 'ipsum'])
+            ->willReturn('Rendered content');
+
+        $renderer->addRenderer($mockRenderer);
+        $data = $renderer->render('foo.template', ['lorem' => 'ipsum']);
+
+        $this->assertEquals('Rendered content', $data);
+    }
+
+    public function testError()
+    {
+        $renderer = new Renderer();
+
+        $loggerMock = $this->getMockForAbstractClass(LoggerInterface::class);
+        $loggerMock
+            ->expects($this->once())
+            ->method('error');
+
+        $renderer->setLogger($loggerMock);
+
+        $data = $renderer->render('testing.template');
+        $this->assertEquals('', $data);
+    }
+}