Add assertOutputNotContains()

It is helpful to be able to ensure output did not get created sometimes.

src/TestSuite/ConsoleIntegrationTestCase.php

@@ -162,6 +162,18 @@ abstract class ConsoleIntegrationTestCase extends TestCase
         $output = implode(PHP_EOL, $this->_out->messages());
         $this->assertContains($expected, $output, $message);
     }
+    /**
+     * Asserts `stdout` does not contain expected output
+     *
+     * @param string $expected Expected output
+     * @param string $message Failure message
+     * @return void
+     */
+    public function assertOutputNotContains($expected, $message = '')
+    {
+        $output = implode(PHP_EOL, $this->_out->messages());
+        $this->assertNotContains($expected, $output, $message);
+    }
 
     /**
      * Asserts `stdout` contains expected regexp