- Rewrites the CSS styles processor/renderer class

- Adds unit tests

tests/unit/Form/Util/StylesTest.php

@@ -0,0 +1,28 @@
+<?php
+
+use MailPoet\Form\Util\Styles;
+
+class StylesTest extends MailPoetTest {
+  function testItSetsDefaultCSSStyles() {
+    expect(property_exists('MailPoet\Form\Util\Styles', 'default_styles'))->true();
+    expect(Styles::$default_styles)->notEmpty();
+  }
+
+  function testItProcessesAndRendersStyles() {
+    $stylesheet = '
+    /* some comment */
+    input[name=first_name]    , input.some_class,     .some_class { color: red  ; background: blue; } .another_style { fonT-siZe: 20px                            }
+    ';
+    $style_processer = new Styles($stylesheet);
+    $extracted_and_prefixed_styles = $style_processer->render($prefix = 'mailpoet');
+    // 1. comments should be stripped
+    // 2. each selector should be refixed
+    // 3. multiple spaces, missing semicolons should be fixed
+    // 4. each style should be on a separate line
+    $expected_result = <<<EOL
+mailpoet input[name=first_name], mailpoet input.some_class, mailpoet .some_class { color: red; background: blue; }
+mailpoet .another_style { font-size: 20px; }
+EOL;
+    expect($extracted_and_prefixed_styles)->equals($expected_result);
+  }
+}