Revert "Fix unit tests"

This reverts commit 28c06b7.

Author: mikehaertl

tests/CommandTest.php

@@ -132,7 +132,7 @@ public function testCanNotRunNotExistantCommand()
         $this->assertFalse($command->execute());
         $this->assertFalse($command->getExecuted());
         $this->assertNotEmpty($command->getError());
-        $this->assertEmpty($command->getStdErr());
+        $this->assertNotEmpty($command->getStdErr());
         $this->assertEmpty($command->getOutput());
         $this->assertEquals(127, $command->getExitCode());
     }
@@ -143,7 +143,7 @@ public function testCanNotRunInvalidCommand()
         $this->assertFalse($command->execute());
         $this->assertFalse($command->getExecuted());
         $this->assertNotEmpty($command->getError());
-        $this->assertEmpty($command->getStdErr());
+        $this->assertNotEmpty($command->getStdErr());
         $this->assertEmpty($command->getOutput());
         $this->assertEquals(2, $command->getExitCode());
     }