Show origin of warning in error message

src/Codeception/Subscriber/ErrorHandler.php

@@ -80,7 +80,8 @@ public function errorHandler($errno, $errstr, $errfile, $errline, $context = arr
             return false;
         }
 
-        throw new \PHPUnit\Framework\Exception($errstr, $errno);
+        $relativePath = codecept_relative_path($errfile);
+        throw new \PHPUnit\Framework\Exception("$errstr at $relativePath:$errline", $errno);
     }
 
     public function shutdownHandler()

tests/unit/Codeception/Subscriber/ErrorHandlerTest.php

@@ -5,8 +5,20 @@
 use Codeception\Subscriber\ErrorHandler;
 use Codeception\Suite;
 
-class ErrorHandlerTest extends \PHPUnit\Framework\TestCase
+class ErrorHandlerTest extends \Codeception\PHPUnit\TestCase
 {
+    private $originalErrorLevel;
+
+    public function _setUp()
+    {
+        $this->originalErrorLevel = error_reporting();
+    }
+
+    public function _tearDown()
+    {
+        // Deprecation message test changes error_level
+        error_reporting($this->originalErrorLevel);
+    }
 
     public function testDeprecationMessagesRespectErrorLevelSetting()
     {
@@ -23,4 +35,16 @@ public function testDeprecationMessagesRespectErrorLevelSetting()
 
         $this->assertEquals([], Notification::all(), 'Deprecation message was added to notifications');
     }
+
+    public function testShowsLocationOfWarning()
+    {
+        if (PHP_MAJOR_VERSION === 5) {
+            $this->expectException(\PHPUnit_Framework_Exception::class);
+        } else {
+            $this->expectException(\PHPUnit\Framework\Exception::class);
+        }
+        $SEP = DIRECTORY_SEPARATOR;
+        $this->expectExceptionMessage("Undefined variable: file at tests{$SEP}unit{$SEP}Codeception{$SEP}Subscriber{$SEP}ErrorHandlerTest.php:48");
+        trigger_error('Undefined variable: file', E_USER_WARNING);
+    }
 }