Fixed bugs in the tests

src/FFMpeg/Filters/Waveform/WaveformFilters.php

@@ -31,7 +31,7 @@ class WaveformFilters
      */
     public function setDownmix()
     {
-        $this->waveform->addFilter(new DownmixFilter());
+        $this->waveform->addFilter(new WaveformDownmixFilter());
 
         return $this;
     }

tests/Unit/Filters/Waveform/WaveformFiltersTest.php

@@ -9,7 +9,7 @@ class WaveformFiltersTest extends TestCase
 {
     public function testResize()
     {
-        $Waveform = $this->createMock(Waveform::class);
+        $Waveform = $this->getWaveformMock();
         $filters = new WaveformFilters($Waveform);
 
         $Waveform->expects($this->once())

tests/Unit/TestCase.php

@@ -47,6 +47,13 @@ class TestCase extends \PHPUnit_Framework_TestCase
             ->getMock();
     }
 
+    public function getWaveformMock()
+    {
+        return $this->getMockBuilder('FFMpeg\Media\Waveform')
+            ->disableOriginalConstructor()
+            ->getMock();
+    }
+
     public function getFFMpegDriverMock()
     {
         return $this->getMockBuilder('FFMpeg\Driver\FFMpegDriver')