Add LoggerState to disble user-configured logging during PHPUnit tests

_config/tests.yml

@@ -11,6 +11,7 @@ SilverStripe\Core\Injector\Injector:
         fixtures: '%$SilverStripe\Dev\State\FixtureTestState'
         requirements: '%$SilverStripe\View\Dev\RequirementsTestState'
         ssviewer: '%$SilverStripe\View\Dev\SSViewerTestState'
+        logstate: '%$SilverStripe\Dev\State\LoggerState'
 ---
 Name: kerneltest
 Before: '*'

src/Dev/State/LoggerState.php

@@ -0,0 +1,42 @@
+<?php
+
+namespace SilverStripe\Dev\State;
+
+use Monolog\Handler\NullHandler;
+use Monolog\Logger;
+use Psr\Log\LoggerInterface;
+use SilverStripe\Core\Injector\Injector;
+use SilverStripe\Dev\SapphireTest;
+
+/**
+ * Disables any user configured loggers by pushing a NullHandler during PHPUnit tests.
+ *
+ * This is designed specifically for Monolog. If using another PSR-3 compatible logging package, this will
+ * not do anything.
+ */
+class LoggerState implements TestState
+{
+    public function setUp(SapphireTest $test)
+    {
+        /** @var Logger $userLogger */
+        $userLogger = Injector::inst()->get(LoggerInterface::class);
+        if ($userLogger && $userLogger instanceof Logger) {
+            $userLogger->setHandlers([new NullHandler()]);
+        }
+    }
+
+    public function tearDown(SapphireTest $test)
+    {
+        // noop
+    }
+
+    public function setUpOnce($class)
+    {
+        // noop
+    }
+
+    public function tearDownOnce($class)
+    {
+        // noop
+    }
+}