[feature] access/assert against stderr output

README.md

@@ -49,8 +49,10 @@ class CreateUserCommandTest extends KernelTestCase
             ->assertSuccessful()
             ->assertStatusCode(0) // equivalent to ->assertSuccessful()
             ->assertOutputContains('Creating admin user "kbond"')
-            ->dump() // dump() the status code/output and continue
-            ->dd() // dd() the status code/output
+            ->assertErrorOutputContains('this is in stderr')
+            ->assertErrorOutputNotContains('admin user')
+            ->dump() // dump() the status code/outputs and continue
+            ->dd() // dd() the status code/outputs
         ;
 
         // testing interactive commands
@@ -67,6 +69,13 @@ class CreateUserCommandTest extends KernelTestCase
             ->assertSuccessful()
             ->assertOutputContains('Creating regular user "kbond"')
         ;
+
+        // access result
+        $result = $this->executeConsoleCommand('create:user');
+
+        $result->statusCode();
+        $result->output(); 
+        $result->errorOutput(); 
     }
 }
 ```
@@ -95,8 +104,10 @@ class CreateUserCommandTest extends TestCase
             ->assertSuccessful()
             ->assertStatusCode(0) // equivalent to ->assertSuccessful()
             ->assertOutputContains('Creating admin user "kbond"')
-            ->dump() // dump() the status code/output and continue
-            ->dd() // dd() the status code/output
+            ->assertErrorOutputContains('this is in stderr')
+            ->assertErrorOutputNotContains('admin user')
+            ->dump() // dump() the status code/outputs and continue
+            ->dd() // dd() the status code/outputs
         ;
 
         // testing interactive commands
@@ -107,6 +118,13 @@ class CreateUserCommandTest extends TestCase
             ->assertSuccessful()
             ->assertOutputContains('Creating regular user "kbond"')
         ;
+
+        // access result
+        $result = TestCommand::for(new CreateUserCommand(/** args... */))->execute();
+
+        $result->statusCode();
+        $result->output(); 
+        $result->errorOutput(); 
     }
 }
 ```

src/CommandResult.php

@@ -12,14 +12,16 @@ final class CommandResult
 {
     private int $statusCode;
     private string $output;
+    private string $errorOutput;
 
     /**
      * @internal
      */
-    public function __construct(int $statusCode, string $output)
+    public function __construct(int $statusCode, string $output, string $errorOutput)
     {
         $this->statusCode = $statusCode;
         $this->output = $output;
+        $this->errorOutput = $errorOutput;
     }
 
     public function statusCode(): int
@@ -32,6 +34,11 @@ public function output(): string
         return $this->output;
     }
 
+    public function errorOutput(): string
+    {
+        return $this->errorOutput;
+    }
+
     public function assertOutputContains(string $expected): self
     {
         PHPUnit::assertStringContainsString($expected, $this->output());
@@ -46,6 +53,20 @@ public function assertOutputNotContains(string $expected): self
         return $this;
     }
 
+    public function assertErrorOutputContains(string $expected): self
+    {
+        PHPUnit::assertStringContainsString($expected, $this->errorOutput());
+
+        return $this;
+    }
+
+    public function assertErrorOutputNotContains(string $expected): self
+    {
+        PHPUnit::assertStringNotContainsString($expected, $this->errorOutput());
+
+        return $this;
+    }
+
     public function assertSuccessful(): self
     {
         return $this->assertStatusCode(0);
@@ -62,6 +83,7 @@ public function dump(): self
     {
         VarDumper::dump("Status: {$this->statusCode()}");
         VarDumper::dump($this->output());
+        VarDumper::dump($this->errorOutput());
 
         return $this;
     }

src/CommandTester.php

@@ -41,11 +41,12 @@ public function execute(): CommandResult
         $this->initOutput([
             'decorated' => true === $this->input->hasParameterOption(['--ansi'], true),
             'verbosity' => $this->verbosity(),
+            'capture_stderr_separately' => true,
         ]);
 
         $statusCode = $this->command->run($this->input, $this->output);
 
-        return new CommandResult($statusCode, $this->getDisplay());
+        return new CommandResult($statusCode, $this->getDisplay(), $this->getErrorOutput());
     }
 
     private function verbosity(): int

tests/Fixture/FixtureCommand.php

@@ -6,6 +6,7 @@
 use Symfony\Component\Console\Input\InputArgument;
 use Symfony\Component\Console\Input\InputInterface;
 use Symfony\Component\Console\Input\InputOption;
+use Symfony\Component\Console\Output\ConsoleOutputInterface;
 use Symfony\Component\Console\Output\OutputInterface;
 use Symfony\Component\Console\Question\Question;
 
@@ -31,9 +32,12 @@ protected function configure(): void
 
     protected function execute(InputInterface $input, OutputInterface $output)
     {
+        $errOutput = $output instanceof ConsoleOutputInterface ? $output->getErrorOutput() : $output;
+
         $output->writeln('Executing <info>command</info>...');
         $output->writeln("verbosity: {$output->getVerbosity()}");
         $output->writeln('decorated: '.($output->isDecorated() ? 'yes' : 'no'));
+        $errOutput->writeln('Error output.');
 
         if ($input->getOption('throw')) {
             throw new \RuntimeException('Exception thrown!');

tests/FunctionalTest.php

@@ -24,6 +24,9 @@ public function string_command_with_no_arguments(): void
             ->assertOutputContains('Executing command')
             ->assertOutputNotContains('arg1')
             ->assertOutputNotContains('opt1')
+            ->assertOutputNotContains('Error output')
+            ->assertErrorOutputContains('Error output')
+            ->assertErrorOutputNotContains('Executing command')
         ;
     }
 

tests/UnitTest.php

@@ -21,6 +21,9 @@ public function command_with_no_arguments(): void
             ->assertOutputContains('Executing command')
             ->assertOutputNotContains('arg1')
             ->assertOutputNotContains('opt1')
+            ->assertOutputNotContains('Error output')
+            ->assertErrorOutputContains('Error output')
+            ->assertErrorOutputNotContains('Executing command')
         ;
     }