Tests: add generic IOTestCase

... with a helper method to retrieve `stdout`, `stderr` and the exit code of a command line command run for use in follow-up assertions.

The `IOTestCase` has full access to all polyfill traits from the PHPUnit Polyfills.

Author: jrfnl

Tests/IOTestCase.php

@@ -0,0 +1,73 @@
+<?php
+/**
+ * PHPCSDevTools, tools for PHP_CodeSniffer sniff developers.
+ *
+ * @package   PHPCSDevTools
+ * @copyright 2019 PHPCSDevTools Contributors
+ * @license   https://opensource.org/licenses/LGPL-3.0 LGPL3
+ * @link      https://github.com/PHPCSStandards/PHPCSDevTools
+ */
+
+namespace PHPCSDevTools\Tests;
+
+use Yoast\PHPUnitPolyfills\TestCases\XTestCase;
+
+/**
+ * Abstract test case for checking the output of command execution.
+ */
+abstract class IOTestCase extends XTestCase
+{
+
+    /**
+     * Helper function to execute a CLI command and retrieve the results.
+     *
+     * @param string      $command    The CLI command to execute.
+     * @param string|null $workingDir Optional. The directory in which to execute the command.
+     *                                Defaults to `null` = the working directory of the current PHP process.
+     *                                Note: if the command itself already contains a "working directory" argument,
+     *                                this parameter will normally not need to be passed.
+     *
+     * @return array Format:
+     *               'exitcode' int    The exit code from the command.
+     *               'stdout'   string The output send to stdout.
+     *               'stderr'   string The output send to stderr.
+     *
+     * @throws \RuntimeException When the passed arguments do not comply.
+     * @throws \RuntimeException When no resource could be obtained to execute the command.
+     */
+    protected function executeCliCommand($command, $workingDir = null)
+    {
+        if (\is_string($command) === false || $command === '') {
+            throw new RuntimeException('Command must be a non-empty string.');
+        }
+
+        if (\is_null($workingDir) === false && (\is_string($workingDir) === false || $workingDir === '')) {
+            throw new RuntimeException('Working directory must be a non-empty string or null.');
+        }
+
+        $descriptorspec = [
+            0 => ['pipe', 'r'],  // stdin
+            1 => ['pipe', 'w'],  // stdout
+            2 => ['pipe', 'w'],  // stderr
+        ];
+
+        $process = \proc_open($command, $descriptorspec, $pipes, $workingDir);
+
+        if (\is_resource($process) === false) {
+            throw new RuntimeException('Could not obtain a resource with proc_open() to execute the command.');
+        }
+
+        $result = [];
+        \fclose($pipes[0]);
+
+        $result['stdout'] = \stream_get_contents($pipes[1]);
+        \fclose($pipes[1]);
+
+        $result['stderr'] = \stream_get_contents($pipes[2]);
+        \fclose($pipes[2]);
+
+        $result['exitcode'] = \proc_close($process);
+
+        return $result;
+    }
+}