diff --git a/src/Generator.php b/src/Generator.php
index 168dbfe3..ecfa747f 100644
--- a/src/Generator.php
+++ b/src/Generator.php
@@ -24,6 +24,10 @@ class Generator
      */
     private $steps;
 
+    /**
+     * @param Filesystem      $filesystem
+     * @param StepInterface[] $steps
+     */
     public function __construct(Filesystem $filesystem, array $steps)
     {
         $this->filesystem = $filesystem;
diff --git a/tests/UnitTest/GeneratorTest.php b/tests/UnitTest/GeneratorTest.php
new file mode 100644
index 00000000..b51d96d4
--- /dev/null
+++ b/tests/UnitTest/GeneratorTest.php
@@ -0,0 +1,55 @@
+<?php
+
+namespace Couscous\Tests\UnitTest;
+
+use Couscous\Generator;
+use Couscous\Model\Repository;
+use Couscous\Tests\UnitTest\Mock\MockRepository;
+use Symfony\Component\Console\Output\NullOutput;
+use Symfony\Component\Console\Output\OutputInterface;
+use Symfony\Component\Filesystem\Filesystem;
+
+/**
+ * @covers \Couscous\Generator
+ */
+class GeneratorTest extends \PHPUnit_Framework_TestCase
+{
+    /**
+     * @test
+     */
+    public function it_should_invoke_every_step()
+    {
+        $filesystem = $this->createFileSystem();
+        $repository = new MockRepository();
+        $output = new NullOutput();
+
+        $steps = [
+            $this->createStep($repository, $output),
+            $this->createStep($repository, $output),
+            $this->createStep($repository, $output),
+        ];
+
+        $generator = new Generator($filesystem, $steps);
+
+        $generator->generate($repository, $output);
+    }
+
+    /**
+     * @return \PHPUnit_Framework_MockObject_MockObject|Filesystem
+     */
+    private function createFilesystem()
+    {
+        return $this->getMock('Symfony\Component\Filesystem\Filesystem');
+    }
+
+    private function createStep(Repository $repository, OutputInterface $output)
+    {
+        $step = $this->getMockForAbstractClass('Couscous\Step\StepInterface');
+
+        $step->expects($this->once())
+            ->method('__invoke')
+            ->with($repository, $output);
+
+        return $step;
+    }
+}
diff --git a/tests/UnitTest/Model/RepositoryTest.php b/tests/UnitTest/Model/RepositoryTest.php
new file mode 100644
index 00000000..c2d3b799
--- /dev/null
+++ b/tests/UnitTest/Model/RepositoryTest.php
@@ -0,0 +1,84 @@
+<?php
+
+namespace Couscous\Tests\UnitTest\Model;
+
+use Couscous\Model\File;
+use Couscous\Model\File\HtmlFile;
+use Couscous\Model\File\MarkdownFile;
+use Couscous\Model\Repository;
+
+/**
+ * @covers \Couscous\Model\Repository
+ */
+class RepositoryTest extends \PHPUnit_Framework_TestCase
+{
+    /**
+     * @test
+     */
+    public function it_should_contain_files()
+    {
+        $repository = new Repository('source', 'target');
+
+        $file1 = $this->createFile('file1');
+        $file2 = $this->createFile('file2');
+
+        $repository->addFile($file1);
+        $repository->addFile($file2);
+        $expected = [
+            'file1' => $file1,
+            'file2' => $file2,
+        ];
+        $this->assertSame($expected, $repository->getFiles());
+
+        $repository->removeFile($file1);
+        $this->assertSame(['file2' => $file2], $repository->getFiles());
+
+        $repository->removeFile($file2);
+        $this->assertSame([], $repository->getFiles());
+    }
+
+    /**
+     * @test
+     */
+    public function replace_should_replace_files()
+    {
+        $repository = new Repository('source', 'target');
+
+        $file1 = $this->createFile('file1');
+        $file2 = $this->createFile('file2');
+
+        $repository->addFile($file1);
+        $this->assertSame(['file1' => $file1], $repository->getFiles());
+
+        $repository->replaceFile($file1, $file2);;
+        $this->assertSame(['file2' => $file2], $repository->getFiles());
+    }
+
+    /**
+     * @test
+     */
+    public function it_should_return_files_by_type()
+    {
+        $repository = new Repository('source', 'target');
+
+        $file1 = new MarkdownFile('file1', 'Hello');
+        $file2 = new HtmlFile('file2', 'Hello');
+
+        $repository->addFile($file1);
+        $repository->addFile($file2);
+
+        $markdownFiles = $repository->findFilesByType('Couscous\Model\File\MarkdownFile');
+        $this->assertSame(['file1' => $file1], $markdownFiles);
+
+        $htmlFiles = $repository->findFilesByType('Couscous\Model\File\HtmlFile');
+        $this->assertSame(['file2' => $file2], $htmlFiles);
+    }
+
+    /**
+     * @return \PHPUnit_Framework_MockObject_MockObject|File
+     */
+    private function createFile($name)
+    {
+        return $this->getMockForAbstractClass('Couscous\Model\File', [$name]);
+    }
+}