diff --git a/src/Controllers/CSSGeneratorController.php b/src/Controllers/CSSGeneratorController.php
index 883e1a7..41b7e7f 100644
--- a/src/Controllers/CSSGeneratorController.php
+++ b/src/Controllers/CSSGeneratorController.php
@@ -89,7 +89,7 @@ public function __invoke(ServerRequestInterface $request, ResponseInterface $res
      *  ]
      * </pre>
      * @throws \InvalidArgumentException If the parameter value is formatted badly. The message may be sent back to the
-     *     client.
+     *  client.
      */
     protected function parseFamilyParameter(string $value): array
     {
@@ -121,8 +121,8 @@ protected function parseFamilyParameter(string $value): array
      *
      * @param mixed $fontDisplay Parameter value
      * @return string Valid font-display css value, or empty string, if $fontDisplay is null or empty.
-     * @throws \InvalidArgumentException If the parameter set, but has not valid value. The message may be sent
-     *          back to the client.
+     * @throws \InvalidArgumentException If the parameter set, but has not valid value. The message may be sent back to
+     *  the client.
      */
     protected function parseDisplayParameter($fontDisplay): string
     {
diff --git a/tests/Functional/CssGeneratorTest.php b/tests/Functional/CssGeneratorTest.php
index 0c2c9e8..19c1296 100644
--- a/tests/Functional/CssGeneratorTest.php
+++ b/tests/Functional/CssGeneratorTest.php
@@ -13,27 +13,81 @@ class CssGeneratorTest extends FunctionalTestCase
      */
     public function testHeaders()
     {
-        $response = $this->runApp('GET', '/css?family=Open+Sans:400,700');
+        $response = $this->runApp('GET', '/css?family=Open+Sans');
 
         $this->assertEquals(200, $response->getStatusCode());
         $this->assertTrue((bool)preg_match('~^text/css(;|$)~', $response->getHeaderLine('Content-Type')));
         $this->assertTrue($response->hasHeader('Cache-Control'));
         $this->assertTrue($response->hasHeader('Pragma'));
+    }
+
+    /**
+     * Test the controller `family` parameter parsing
+     */
+    public function testFamilyParsing()
+    {
+        $app = $this->makeApp();
+        $container = $app->getContainer();
+        $container['webfontCSSGenerator'] = function () {
+            $generator = \Mockery::mock(WebfontCSSGenerator::class);
+            $generator->shouldReceive('makeCSS')
+                ->once()
+                ->with(['Roboto' => ['400']], '')
+                ->andReturn('');
+            $generator->shouldReceive('makeCSS')
+                ->once()
+                ->with([
+                    'Open Sans' => ['400'],
+                    'Roboto' => ['400', '400i', '700i'],
+                ], '')
+                ->andReturn('');
+            return $generator;
+        };
+
+        $this->assertEquals(200, $this->runSpecificApp($app, 'GET', '/css?family=Roboto')->getStatusCode());
+        $this->assertEquals(200, $this->runSpecificApp($app, 'GET', '/css?family=Open+Sans|Roboto:400,400i,700i')->getStatusCode());
 
-        $this->assertEquals(200, $this->runApp('GET', '/css?family=Open+Sans')->getStatusCode());
+        $this->assertEquals(422, $this->runSpecificApp($app, 'GET', '/css?family=')->getStatusCode());
+        $this->assertEquals(422, $this->runSpecificApp($app, 'GET', '/css?family=|Open+Sans:400,700')->getStatusCode());
+        $this->assertEquals(422, $this->runSpecificApp($app, 'GET', '/css?family=:400,700')->getStatusCode());
+        $this->assertEquals(422, $this->runSpecificApp($app, 'GET', '/css')->getStatusCode());
     }
 
     /**
-     * Tests that the route returns an client error status with bad requests
+     * Test the controller `display` parameter parsing
      */
-    public function testBadRequests()
+    public function testDisplayParsing()
     {
-        $this->assertEquals(422, $this->runApp('GET', '/css?family=')->getStatusCode());
-        $this->assertEquals(422, $this->runApp('GET', '/css?family=|Open+Sans:400,700')->getStatusCode());
-        $this->assertEquals(422, $this->runApp('GET', '/css?family=:400,700')->getStatusCode());
-        $this->assertEquals(422, $this->runApp('GET', '/css')->getStatusCode());
-        $this->assertEquals(422, $this->runApp('GET', '/css?family=Open+Sans:400,700&display[]=bad')->getStatusCode());
+        $app = $this->makeApp();
+        $container = $app->getContainer();
+        $container['webfontCSSGenerator'] = function () {
+            $generator = \Mockery::mock(WebfontCSSGenerator::class);
+            $generator->shouldReceive('makeCSS')
+                ->once()
+                ->with(['Open Sans' => ['400']], '')
+                ->andReturn('');
+            $generator->shouldReceive('makeCSS')
+                ->once()
+                ->with(['Open Sans' => ['400']], '')
+                ->andReturn('');
+            $generator->shouldReceive('makeCSS')
+                ->once()
+                ->with(['Open Sans' => ['400']], 'swap')
+                ->andReturn('');
+            return $generator;
+        };
 
+        $this->assertEquals(200, $this->runSpecificApp($app, 'GET', '/css?family=Open+Sans')->getStatusCode());
+        $this->assertEquals(200, $this->runSpecificApp($app, 'GET', '/css?family=Open+Sans&display=')->getStatusCode());
+        $this->assertEquals(200, $this->runSpecificApp($app, 'GET', '/css?family=Open+Sans&display=swap')->getStatusCode());
+        $this->assertEquals(422, $this->runSpecificApp($app, 'GET', '/css?family=Open+Sans&display[]=bad')->getStatusCode());
+    }
+
+    /**
+     * Test handling errors from webfontCSSGenerator
+     */
+    public function testGeneratorInputError()
+    {
         $app = $this->makeApp();
         $container = $app->getContainer();
         $container['webfontCSSGenerator'] = function () {
@@ -42,7 +96,7 @@ public function testBadRequests()
             return $generator;
         };
 
-        $this->assertEquals(422, $this->runSpecificApp($app, 'GET', '/css?family=Open+Sans:400,700')->getStatusCode());
+        $this->assertEquals(422, $this->runSpecificApp($app, 'GET', '/css?family=Open+Sans')->getStatusCode());
     }
 
     /**