Add ReadEnvVarCommand test

module/CLI/src/Command/Config/ReadEnvVarCommand.php

@@ -4,6 +4,7 @@ declare(strict_types=1);
 
 namespace Shlinkio\Shlink\CLI\Command\Config;
 
+use Closure;
 use Shlinkio\Shlink\CLI\Util\ExitCode;
 use Shlinkio\Shlink\Core\Config\EnvVars;
 use Symfony\Component\Console\Command\Command;
@@ -22,6 +23,15 @@ class ReadEnvVarCommand extends Command
 {
     public const NAME = 'env-var:read';
 
+    /** @var Closure(string $envVar): mixed */
+    private readonly Closure $loadEnvVar;
+
+    public function __construct(?Closure $loadEnvVar = null)
+    {
+        $this->loadEnvVar = $loadEnvVar ?? static fn (string $envVar) => EnvVars::from($envVar)->loadFromEnv();
+        parent::__construct();
+    }
+
     protected function configure(): void
     {
         $this
@@ -51,7 +61,7 @@ class ReadEnvVarCommand extends Command
     protected function execute(InputInterface $input, OutputInterface $output): int
     {
         $envVar = $input->getArgument('envVar');
-        $output->writeln(formatEnvVarValue(EnvVars::from($envVar)->loadFromEnv()));
+        $output->writeln(formatEnvVarValue(($this->loadEnvVar)($envVar)));
 
         return ExitCode::EXIT_SUCCESS;
     }

module/CLI/test/Command/Config/ReadEnvVarCommandTest.php

@@ -0,0 +1,54 @@
+<?php
+
+declare(strict_types=1);
+
+namespace ShlinkioTest\Shlink\CLI\Command\Config;
+
+use Monolog\Test\TestCase;
+use PHPUnit\Framework\Attributes\Test;
+use Shlinkio\Shlink\CLI\Command\Config\ReadEnvVarCommand;
+use Shlinkio\Shlink\Core\Config\EnvVars;
+use ShlinkioTest\Shlink\CLI\Util\CliTestUtils;
+use Symfony\Component\Console\Exception\InvalidArgumentException;
+use Symfony\Component\Console\Tester\CommandTester;
+
+class ReadEnvVarCommandTest extends TestCase
+{
+    private CommandTester $commandTester;
+    private string $envVarValue = 'the_env_var_value';
+
+    protected function setUp(): void
+    {
+        $this->commandTester = CliTestUtils::testerForCommand(new ReadEnvVarCommand(fn () => $this->envVarValue));
+    }
+
+    #[Test]
+    public function errorIsThrownIfProvidedEnvVarIsInvalid(): void
+    {
+        $this->expectException(InvalidArgumentException::class);
+        $this->expectExceptionMessage('foo is not a valid Shlink environment variable');
+
+        $this->commandTester->execute(['envVar' => 'foo']);
+    }
+
+    #[Test]
+    public function valueIsPrintedIfProvidedEnvVarIsValid(): void
+    {
+        $this->commandTester->execute(['envVar' => EnvVars::BASE_PATH->value]);
+        $output = $this->commandTester->getDisplay();
+
+        self::assertStringNotContainsString('Select the env var to read', $output);
+        self::assertStringContainsString($this->envVarValue, $output);
+    }
+
+    #[Test]
+    public function envVarNameIsRequestedIfArgumentIsMissing(): void
+    {
+        $this->commandTester->setInputs([EnvVars::BASE_PATH->value]);
+        $this->commandTester->execute([]);
+        $output = $this->commandTester->getDisplay();
+
+        self::assertStringContainsString('Select the env var to read', $output);
+        self::assertStringContainsString($this->envVarValue, $output);
+    }
+}