Add expectErrorLog() for expecting error_log() output

src/Framework/TestCase.php

@@ -22,9 +22,11 @@
 use function defined;
 use function error_clear_last;
 use function explode;
+use function fclose;
 use function getcwd;
 use function implode;
 use function in_array;
+use function ini_set;
 use function is_array;
 use function is_callable;
 use function is_int;
@@ -38,12 +40,16 @@
 use function ob_get_level;
 use function ob_start;
 use function preg_match;
+use function preg_replace;
 use function restore_error_handler;
 use function restore_exception_handler;
 use function set_error_handler;
 use function set_exception_handler;
 use function sprintf;
 use function str_contains;
+use function stream_get_contents;
+use function stream_get_meta_data;
+use function tmpfile;
 use function trim;
 use AssertionError;
 use DeepCopy\DeepCopy;
@@ -175,6 +181,7 @@ abstract class TestCase extends Assert implements Reorderable, SelfDescribing, T
     private int $outputBufferingLevel;
     private bool $outputRetrievedForAssertion = false;
     private bool $doesNotPerformAssertions    = false;
+    private bool $expectErrorLog              = false;
 
     /**
      * @var list<Comparator>
@@ -1005,6 +1012,11 @@ final protected function expectOutputString(string $expectedString): void
         $this->outputExpectedString = $expectedString;
     }
 
+    final protected function expectErrorLog(): void
+    {
+        $this->expectErrorLog = true;
+    }
+
     /**
      * @param class-string<Throwable> $exception
      */
@@ -1104,8 +1116,20 @@ final protected function runTest(): mixed
     {
         $testArguments = array_merge($this->data, array_values($this->dependencyInput));
 
+        $capture          = tmpfile();
+        $errorLogPrevious = ini_set('error_log', stream_get_meta_data($capture)['uri']);
+
         try {
             $testResult = $this->{$this->methodName}(...$testArguments);
+
+            $errorLogOutput = stream_get_contents($capture);
+
+            if ($this->expectErrorLog) {
+                $this->assertNotEmpty($errorLogOutput, 'Test did not call error_log().');
+            } else {
+                // strip date from logged error, see https://github.com/php/php-src/blob/c696087e323263e941774ebbf902ac249774ec9f/main/main.c#L905
+                print preg_replace('/\[.+\] /', '', $errorLogOutput);
+            }
         } catch (Throwable $exception) {
             if (!$this->shouldExceptionExpectationsBeVerified($exception)) {
                 throw $exception;
@@ -1114,6 +1138,12 @@ final protected function runTest(): mixed
             $this->verifyExceptionExpectations($exception);
 
             return null;
+        } finally {
+            if ($capture !== false) {
+                fclose($capture);
+            }
+
+            ini_set('error_log', $errorLogPrevious);
         }
 
         $this->expectedExceptionWasNotRaised();

tests/end-to-end/generic/_files/ExpectErrorLogFailTest.php

@@ -0,0 +1,31 @@
+<?php declare(strict_types=1);
+/*
+ * This file is part of PHPUnit.
+ *
+ * (c) Sebastian Bergmann <[email protected]>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+namespace PHPUnit\TestFixture\ExpectNoErrorLog;
+
+use PHPUnit\Framework\TestCase;
+
+class FooBar
+{
+    public function doFoo()
+    {
+        return '';
+    }
+}
+
+final class ExpectErrorLogFailTest extends TestCase
+{
+    public function testOne(): void
+    {
+        $foo = new FooBar;
+
+        $this->assertSame('', $foo->doFoo());
+        $this->expectErrorLog();
+    }
+}

tests/end-to-end/generic/_files/ExpectErrorLogTest.php

@@ -0,0 +1,34 @@
+<?php declare(strict_types=1);
+/*
+ * This file is part of PHPUnit.
+ *
+ * (c) Sebastian Bergmann <[email protected]>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+namespace PHPUnit\TestFixture\ExpectErrorLog;
+
+use function error_log;
+use PHPUnit\Framework\TestCase;
+
+class Foo
+{
+    public function doFoo()
+    {
+        error_log('logged a side effect');
+
+        return '';
+    }
+}
+
+final class ExpectErrorLogTest extends TestCase
+{
+    public function testOne(): void
+    {
+        $foo = new Foo;
+
+        $this->assertSame('', $foo->doFoo());
+        $this->expectErrorLog();
+    }
+}

tests/end-to-end/generic/expect-error-log-fail.phpt

@@ -0,0 +1,31 @@
+--TEST--
+https://github.com/sebastianbergmann/phpunit/issues/2155
+--FILE--
+<?php declare(strict_types=1);
+$_SERVER['argv'][] = '--do-not-cache-result';
+$_SERVER['argv'][] = '--no-configuration';
+$_SERVER['argv'][] = '--testdox';
+$_SERVER['argv'][] = __DIR__ . '/_files/ExpectErrorLogFailTest.php';
+
+require_once __DIR__ . '/../../bootstrap.php';
+
+(new PHPUnit\TextUI\Application)->run($_SERVER['argv']);
+--EXPECTF--
+PHPUnit %s by Sebastian Bergmann and contributors.
+
+Runtime: %s
+
+F                                                                   1 / 1 (100%)
+
+Time: %s, Memory: %s
+
+Expect Error Log Fail (PHPUnit\TestFixture\ExpectNoErrorLog\ExpectErrorLogFail)
+ ✘ One
+   │
+   │ Test did not call error_log().
+   │ Failed asserting that a string is not empty.
+
+   │
+
+FAILURES!
+Tests: 1, Assertions: 2, Failures: 1.

tests/end-to-end/generic/expect-error-log.phpt

@@ -0,0 +1,25 @@
+--TEST--
+https://github.com/sebastianbergmann/phpunit/issues/2155
+--FILE--
+<?php declare(strict_types=1);
+$_SERVER['argv'][] = '--do-not-cache-result';
+$_SERVER['argv'][] = '--no-configuration';
+$_SERVER['argv'][] = '--testdox';
+$_SERVER['argv'][] = __DIR__ . '/_files/ExpectErrorLogTest.php';
+
+require_once __DIR__ . '/../../bootstrap.php';
+
+(new PHPUnit\TextUI\Application)->run($_SERVER['argv']);
+--EXPECTF--
+PHPUnit %s by Sebastian Bergmann and contributors.
+
+Runtime: %s
+
+.                                                                   1 / 1 (100%)
+
+Time: %s, Memory: %s
+
+Expect Error Log (PHPUnit\TestFixture\ExpectErrorLog\ExpectErrorLog)
+ ✔ One
+
+OK (1 test, 2 assertions)