Fix tests

tests/Monolog/Handler/Slack/SlackRecordTest.php

@@ -12,7 +12,7 @@
 namespace Monolog\Handler\Slack;
 
 use Monolog\Logger;
-use Monolog\TestCase;
+use Monolog\Test\TestCase;
 
 /**
  * @coversDefaultClass Monolog\Handler\Slack\SlackRecord

tests/Monolog/Handler/SlackWebhookHandlerTest.php

@@ -11,7 +11,7 @@
 
 namespace Monolog\Handler;
 
-use Monolog\TestCase;
+use Monolog\Test\TestCase;
 use Monolog\Logger;
 use Monolog\Formatter\LineFormatter;
 use Monolog\Handler\Slack\SlackRecord;

tests/Monolog/Handler/SlackbotHandlerTest.php

@@ -11,7 +11,7 @@
 
 namespace Monolog\Handler;
 
-use Monolog\TestCase;
+use Monolog\Test\TestCase;
 use Monolog\Logger;
 
 /**