diff --git a/src/Util/Logger/StreamLogger.php b/src/Util/Logger/StreamLogger.php
index ad1b152d9e..10ad0a0976 100644
--- a/src/Util/Logger/StreamLogger.php
+++ b/src/Util/Logger/StreamLogger.php
@@ -35,6 +35,12 @@ class StreamLogger extends AbstractFriendicaLogger
 	 */
 	private $pid;
 
+	/**
+	 * An error message
+	 * @var string
+	 */
+	private $errorMessage;
+
 	/**
 	 * Translates LogLevel log levels to integer values
 	 * @var array
@@ -98,7 +104,7 @@ class StreamLogger extends AbstractFriendicaLogger
 	protected function addEntry($level, $message, $context = [])
 	{
 		if (!array_key_exists($level, $this->levelToInt)) {
-			throw new \InvalidArgumentException('The level "%s" is not valid', $level);
+			throw new \InvalidArgumentException(sprintf('The level "%s" is not valid.', $level));
 		}
 
 		$logLevel = $this->levelToInt[$level];
@@ -151,12 +157,14 @@ class StreamLogger extends AbstractFriendicaLogger
 		}
 
 		$this->createDir();
-		$this->stream = fopen($this->url, 'a');
+		set_error_handler([$this, 'customErrorHandler']);
+		$this->stream = fopen($this->url, 'ab');
+		restore_error_handler();
 
 		if (!is_resource($this->stream)) {
 			$this->stream = null;
 
-			throw new \UnexpectedValueException(sprintf('The stream or file "%s" could not be opened.', $this->url));
+			throw new \UnexpectedValueException(sprintf('The stream or file "%s" could not be opened: ' . $this->errorMessage, $this->url));
 		}
 	}
 
@@ -173,10 +181,18 @@ class StreamLogger extends AbstractFriendicaLogger
 		}
 
 		if (isset($dirname) && !is_dir($dirname)) {
+			set_error_handler([$this, 'customErrorHandler']);
 			$status = mkdir($dirname, 0777, true);
+			restore_error_handler();
+
 			if (!$status && !is_dir($dirname)) {
-				throw new \UnexpectedValueException(sprintf('Directory "%s" cannot get created.', $dirname));
+				throw new \UnexpectedValueException(sprintf('Directory "%s" cannot get created: ' . $this->errorMessage, $dirname));
 			}
 		}
 	}
+
+	private function customErrorHandler($code, $msg)
+	{
+		$this->errorMessage = preg_replace('{^(fopen|mkdir)\(.*?\): }', '', $msg);
+	}
 }
diff --git a/tests/src/Util/Logger/StreamLoggerTest.php b/tests/src/Util/Logger/StreamLoggerTest.php
new file mode 100644
index 0000000000..a2e81441b2
--- /dev/null
+++ b/tests/src/Util/Logger/StreamLoggerTest.php
@@ -0,0 +1,203 @@
+<?php
+
+namespace Friendica\Test\src\Util\Logger;
+
+use Friendica\Test\MockedTest;
+use Friendica\Test\Util\VFSTrait;
+use Friendica\Util\Introspection;
+use Friendica\Util\Logger\StreamLogger;
+use Mockery\MockInterface;
+use org\bovigo\vfs\vfsStream;
+use Psr\Log\LogLevel;
+
+class StreamLoggerTest extends MockedTest
+{
+	const LOGLINE = '/\d{4}-\d{2}-\d{2} \d{2}:\d{2}:\d{2} .* \[.*\]: .* \{.*\"file\":\".*\".*,.*\"line\":\d*,.*\"function\":\".*\".*,.*\"uid\":\".*\".*,.*\"process_id\":\d*.*\}/';
+
+	const FILE = 'test';
+	const LINE = 666;
+	const FUNC = 'myfunction';
+
+	use VFSTrait;
+
+	/**
+	 * @var Introspection|MockInterface
+	 */
+	private $introspection;
+
+	protected function setUp()
+	{
+		parent::setUp();
+
+		$this->setUpVfsDir();
+
+		$this->introspection = \Mockery::mock(Introspection::class);
+		$this->introspection->shouldReceive('getRecord')->andReturn([
+			'file'     => self::FILE,
+			'line'     => self::LINE,
+			'function' => self::FUNC
+		]);
+	}
+
+	public function assertLogline($string)
+	{
+		$this->assertRegExp(self::LOGLINE, $string);
+	}
+
+	public function assertLoglineNums($assertNum, $string)
+	{
+		$this->assertEquals($assertNum, preg_match_all(self::LOGLINE, $string));
+	}
+
+	public function testNormal()
+	{
+		$logfile = vfsStream::newFile('friendica.log')
+			->at($this->root);
+
+		$logger = new StreamLogger('test', $logfile->url(), $this->introspection);
+		$logger->emergency('working!');
+		$logger->alert('working too!');
+		$logger->debug('and now?');
+		$logger->notice('message', ['an' => 'context']);
+
+		$text = $logfile->getContent();
+		$this->assertLogline($text);
+		$this->assertLoglineNums(4, $text);
+	}
+
+	/**
+	 * Test if a log entry is correctly interpolated
+	 */
+	public function testPsrInterpolate()
+	{
+		$logfile = vfsStream::newFile('friendica.log')
+			->at($this->root);
+
+		$logger = new StreamLogger('test', $logfile->url(), $this->introspection);
+
+		$logger->emergency('A {psr} test', ['psr' => 'working']);
+		$logger->alert('An {array} test', ['array' => ['it', 'is', 'working']]);
+		$text = $logfile->getContent();
+		$this->assertContains('A working test', $text);
+		$this->assertContains('An ["it","is","working"] test', $text);
+	}
+
+	/**
+	 * Test if a log entry contains all necessary information
+	 */
+	public function testContainsInformation()
+	{
+		$logfile = vfsStream::newFile('friendica.log')
+			->at($this->root);
+
+		$logger = new StreamLogger('test', $logfile->url(), $this->introspection);
+
+		$logger->emergency('A test');
+
+		$text = $logfile->getContent();
+		$this->assertContains('"process_id":' . getmypid(), $text);
+		$this->assertContains('"file":"' . self::FILE . '"', $text);
+		$this->assertContains('"line":' . self::LINE, $text);
+		$this->assertContains('"function":"' . self::FUNC . '"', $text);
+	}
+
+	/**
+	 * Test if the minimum level is working
+	 */
+	public function testMinimumLevel()
+	{
+		$logfile = vfsStream::newFile('friendica.log')
+			->at($this->root);
+
+		$logger = new StreamLogger('test', $logfile->url(), $this->introspection, LogLevel::NOTICE);
+
+		$logger->emergency('working');
+		$logger->alert('working');
+		$logger->error('working');
+		$logger->warning('working');
+		$logger->notice('working');
+		$logger->info('not working');
+		$logger->debug('not working');
+
+		$text = $logfile->getContent();
+
+		$this->assertLoglineNums(5, $text);
+	}
+
+
+	/**
+	 * Test if a file cannot get opened
+	 * @expectedException \UnexpectedValueException
+	 */
+	public function testNoFile()
+	{
+		$logfile = vfsStream::newFile('friendica.log')
+			->at($this->root)
+			->chmod(0);
+
+		$logger = new StreamLogger('test', $logfile->url(), $this->introspection);
+
+		$logger->emergency('not working');
+	}
+
+	/**
+	 * Test when a file isn't set
+	 * @expectedException \LogicException
+	 * @expectedExceptionMessage Missing stream URL.
+	 */
+	public function testNoUrl()
+	{
+		$logger = new StreamLogger('test', '', $this->introspection);
+
+		$logger->emergency('not working');
+	}
+
+	/**
+	 * Test when a file doesn't exist
+	 * @expectedException \UnexpectedValueException
+	 * @expectedExceptionMessageRegExp /The stream or file .* could not be opened: .* /
+	 */
+	public function testWrongUrl()
+	{
+		$logger = new StreamLogger('test', 'wrongfile', $this->introspection);
+
+		$logger->emergency('not working');
+	}
+
+	/**
+	 * Test when the directory cannot get created
+	 * @expectedException \UnexpectedValueException
+	 * @expectedExceptionMessageRegExp /Directory .* cannot get created: .* /
+	 */
+	public function testWrongDir()
+	{
+		$logger = new StreamLogger('test', 'a/wrong/directory/file.txt', $this->introspection);
+
+		$logger->emergency('not working');
+	}
+
+	/**
+	 * Test when the minimum level is not valid
+	 * @expectedException \InvalidArgumentException
+	 * @expectedExceptionMessageRegExp /The level ".*" is not valid./
+	 */
+	public function testWrongMinimumLevel()
+	{
+		$logger = new StreamLogger('test', 'file.text', $this->introspection, 'NOPE');
+	}
+
+	/**
+	 * Test when the minimum level is not valid
+	 * @expectedException \InvalidArgumentException
+	 * @expectedExceptionMessageRegExp /The level ".*" is not valid./
+	 */
+	public function testWrongLogLevel()
+	{
+		$logfile = vfsStream::newFile('friendica.log')
+			->at($this->root);
+
+		$logger = new StreamLogger('test', $logfile->url(), $this->introspection);
+
+		$logger->log('NOPE', 'a test');
+	}
+}