Add new tests, remove redundant code

tests/SPC/builder/unix/UnixSystemUtilTest.php

@@ -0,0 +1,52 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SPC\Tests\builder\unix;
+
+use PHPUnit\Framework\TestCase;
+use SPC\builder\freebsd\SystemUtil as FreebsdSystemUtil;
+use SPC\builder\linux\SystemUtil as LinuxSystemUtil;
+use SPC\builder\macos\SystemUtil as MacosSystemUtil;
+use SPC\exception\FileSystemException;
+
+/**
+ * @internal
+ */
+class UnixSystemUtilTest extends TestCase
+{
+    private FreebsdSystemUtil|LinuxSystemUtil|MacosSystemUtil $util;
+
+    public function setUp(): void
+    {
+        $util_class = match (PHP_OS_FAMILY) {
+            'Linux' => 'SPC\builder\linux\SystemUtil',
+            'Darwin' => 'SPC\builder\macos\SystemUtil',
+            'FreeBSD' => 'SPC\builder\freebsd\SystemUtil',
+            default => null,
+        };
+        if ($util_class === null) {
+            self::markTestIncomplete('This test is only for Unix');
+        }
+        $this->util = new $util_class();
+    }
+
+    /**
+     * @throws FileSystemException
+     */
+    public function testMakeCmakeToolchainFile()
+    {
+        $str = $this->util->makeCmakeToolchainFile(PHP_OS_FAMILY, 'x86_64', '');
+        $this->assertIsString($str);
+    }
+
+    public function testFindCommand()
+    {
+        $this->assertIsString($this->util->findCommand('bash'));
+    }
+
+    public function testMakeEnvVarString()
+    {
+        $this->assertEquals("PATH='/usr/bin' PKG_CONFIG='/usr/bin/pkg-config'", $this->util->makeEnvVarString(['PATH' => '/usr/bin', 'PKG_CONFIG' => '/usr/bin/pkg-config']));
+    }
+}