diff --git a/src/Configuration.php b/src/Configuration.php
index 9eba89f..d43d5ae 100644
--- a/src/Configuration.php
+++ b/src/Configuration.php
@@ -2,10 +2,10 @@
 
 namespace PHRETS;
 
+use PHRETS\Enums\RETSVersion;
 use PHRETS\Exceptions\InvalidConfiguration;
 use PHRETS\Strategies\SimpleStrategy;
 use PHRETS\Strategies\Strategy;
-use PHRETS\Versions\RETSVersion;
 
 class Configuration
 {
@@ -17,22 +17,21 @@ class Configuration
     protected ?string $login_url = null;
     protected string $user_agent = 'PHRETS/2.6.4';
     protected ?string $user_agent_password = null;
-    protected RETSVersion $rets_version;
+    protected readonly RETSVersion $rets_version;
     protected readonly Strategy $strategy;
     protected string $http_authentication = 'digest';
 
     /** @var array<string,mixed> */
     protected array $options = [];
 
-    public function __construct(?Strategy $strategy = null)
-    {
-        if ($strategy === null) {
-            $strategy = new SimpleStrategy();
-        }
+    public function __construct(
+        ?Strategy $strategy = null,
+        ?RETSVersion $version = null
+    ) {
+        $this->rets_version = $version ?? RETSVersion::VERSION_1_5;
+        $this->strategy = $strategy ?? new SimpleStrategy();
 
-        $this->rets_version = (new RETSVersion())->setVersion('1.5');
-        $this->strategy = $strategy;
-        $strategy->initialize($this);
+        $this->strategy->initialize($this);
     }
 
     public function getLoginUrl(): ?string
@@ -66,18 +65,6 @@ public function getRetsVersion(): RETSVersion
         return $this->rets_version;
     }
 
-    /**
-     * @param string $rets_version
-     *
-     * @return $this
-     */
-    public function setRetsVersion(string $rets_version)
-    {
-        $this->rets_version = (new RETSVersion())->setVersion($rets_version);
-
-        return $this;
-    }
-
     public function getUserAgent(): string
     {
         return $this->user_agent;
@@ -140,11 +127,22 @@ public static function load(array $configuration = []): self
             'login_url' => 'LoginUrl',
             'user_agent' => 'UserAgent',
             'user_agent_password' => 'UserAgentPassword',
-            'rets_version' => 'RetsVersion',
             'http_authentication' => 'HttpAuthenticationMethod',
         ];
 
-        $me = new self();
+        $version = null;
+        $retsVersion = $configuration['rets_version'] ?? null;
+        if ($retsVersion !== null && $retsVersion !== '') {
+            if (str_starts_with($retsVersion, 'RETS/')) {
+                $retsVersion = substr($retsVersion, strlen('RETS/'));
+            }
+            $version = RETSVersion::tryFrom($retsVersion);
+            if ($version === null) {
+                throw new InvalidConfiguration('Invalid RETS version: ' . $retsVersion);
+            }
+        }
+
+        $me = new self(version: $version);
 
         foreach ($variables as $k => $m) {
             if (array_key_exists($k, $configuration)) {
@@ -169,7 +167,7 @@ public function valid(): bool
 
     /**
      */
-    public function getStrategy(): \PHRETS\Strategies\Strategy
+    public function getStrategy(): Strategy
     {
         return $this->strategy;
     }
@@ -181,17 +179,12 @@ public function userAgentDigestHash(Session $session): string
         $ua_a1 = md5($this->getUserAgent() . ':' . $this->getUserAgentPassword());
 
         return md5(
-            trim((string) $ua_a1) . '::' . trim((string) $session->getRetsSessionId()) .
-            ':' . trim((string) $this->getRetsVersion()->asHeader())
+            trim($ua_a1) . '::' . trim((string) $session->getRetsSessionId()) .
+            ':' . trim($this->getRetsVersion()->asHeader())
         );
     }
 
-    /**
-     * @param $auth_method
-     *
-     * @return $this
-     */
-    public function setHttpAuthenticationMethod(string $auth_method)
+    public function setHttpAuthenticationMethod(string $auth_method): self
     {
         if (!in_array($auth_method, [self::AUTH_BASIC, self::AUTH_DIGEST])) {
             throw new \InvalidArgumentException("Given authentication method is invalid.  Must be 'basic' or 'digest'");
@@ -201,8 +194,6 @@ public function setHttpAuthenticationMethod(string $auth_method)
         return $this;
     }
 
-    /**
-     */
     public function getHttpAuthenticationMethod(): string
     {
         return $this->http_authentication;
diff --git a/src/Enums/RETSVersion.php b/src/Enums/RETSVersion.php
new file mode 100644
index 0000000..8906228
--- /dev/null
+++ b/src/Enums/RETSVersion.php
@@ -0,0 +1,23 @@
+<?php
+declare(strict_types=1);
+
+namespace PHRETS\Enums;
+
+enum RETSVersion: string
+{
+    case VERSION_1_5 = '1.5';
+    case VERSION_1_7 = '1.7';
+    case VERSION_1_7_1 = '1.7.1';
+    case VERSION_1_7_2 = '1.7.2';
+    case VERSION_1_8 = '1.8';
+
+    public function asHeader(): string
+    {
+        return 'RETS/' . $this->value;
+    }
+
+    public function isAtLeast(self $version): bool
+    {
+        return version_compare($this->value, $version->value) >= 0;
+    }
+}
diff --git a/src/Exceptions/InvalidRETSVersion.php b/src/Exceptions/InvalidRETSVersion.php
deleted file mode 100644
index 19f7895..0000000
--- a/src/Exceptions/InvalidRETSVersion.php
+++ /dev/null
@@ -1,7 +0,0 @@
-<?php
-
-namespace PHRETS\Exceptions;
-
-class InvalidRETSVersion extends \Exception
-{
-}
diff --git a/src/Parsers/GetMetadata/System.php b/src/Parsers/GetMetadata/System.php
index b00a45a..9547e16 100644
--- a/src/Parsers/GetMetadata/System.php
+++ b/src/Parsers/GetMetadata/System.php
@@ -2,6 +2,7 @@
 
 namespace PHRETS\Parsers\GetMetadata;
 
+use PHRETS\Enums\RETSVersion;
 use PHRETS\Http\Response;
 use PHRETS\Models\Metadata\System as SystemModel;
 use PHRETS\Parsers\ParserType;
@@ -22,7 +23,7 @@ public function parse(Session $rets, Response $response): SystemModel
 
         $configuration = $rets->getConfiguration();
 
-        if ($configuration->getRetsVersion()->is1_5()) {
+        if ($configuration->getRetsVersion() === RETSVersion::VERSION_1_5) {
             if (property_exists($base->System, 'SystemID') && $base->System->SystemID !== null) {
                 $metadata->setSystemID((string) $base->System->SystemID);
             }
diff --git a/src/Session.php b/src/Session.php
index 937164b..ca7c3c8 100644
--- a/src/Session.php
+++ b/src/Session.php
@@ -97,8 +97,12 @@ public function Login(): Bulletin
      * @param int $location
      *
      */
-    public function GetPreferredObject(string $resource, string $type, string $content_id, int $location = 0): ?BaseObject
-    {
+    public function GetPreferredObject(
+        string $resource,
+        string $type,
+        string $content_id,
+        int $location = 0
+    ): ?BaseObject {
         $collection = $this->GetObject($resource, $type, $content_id, '0', $location);
 
         return $collection[0] ?? null;
@@ -115,8 +119,13 @@ public function GetPreferredObject(string $resource, string $type, string $conte
      *
      * @throws \PHRETS\Exceptions\CapabilityUnavailable
      */
-    public function GetObject(string $resource, string $type, string $content_ids, string|int $object_ids = '*', $location = 0): array
-    {
+    public function GetObject(
+        string $resource,
+        string $type,
+        string $content_ids,
+        string|int $object_ids = '*',
+        int $location = 0
+    ): array {
         $request_id = GetObject::ids($content_ids, $object_ids);
 
         $response = $this->request(
@@ -476,7 +485,10 @@ protected function request(string $capability, array $options = [], bool $is_ret
                     'headers' => $options['headers'],
                     'body' => $options['body'],
                 ]);
-            } elseif ($this->configuration->readOption('use_post_method') || array_key_exists('form_params', $options)) {
+            } elseif (
+                $this->configuration->readOption('use_post_method') ||
+                array_key_exists('form_params', $options)
+            ) {
                 if (array_key_exists('form_params', $options)) {
                     $this->debug('Using POST method per form_params option');
                     $query = $options['form_params'];
@@ -669,11 +681,6 @@ public function getLastResponse(): string
         return (string) $this->last_response?->getBody();
     }
 
-    public function getClient(): ClientInterface
-    {
-        return $this->client;
-    }
-
     public function getRetsSessionId(): ?string
     {
         return $this->rets_session_id;
diff --git a/src/Strategies/SimpleStrategy.php b/src/Strategies/SimpleStrategy.php
index 5b665f1..32f3c78 100644
--- a/src/Strategies/SimpleStrategy.php
+++ b/src/Strategies/SimpleStrategy.php
@@ -3,6 +3,7 @@
 namespace PHRETS\Strategies;
 
 use PHRETS\Configuration;
+use PHRETS\Enums\RETSVersion;
 use PHRETS\Exceptions\ParserNotFound;
 use PHRETS\Parsers\ParserType;
 
@@ -57,7 +58,7 @@ public function provide(ParserType $parser): mixed
      */
     public function initialize(Configuration $configuration): void
     {
-        if ($configuration->getRetsVersion()->isAtLeast1_8()) {
+        if ($configuration->getRetsVersion()->isAtLeast(RETSVersion::VERSION_1_8)) {
             $this->classes[ParserType::LOGIN->value] = \PHRETS\Parsers\Login\OneEight::class;
             $this->classes[ParserType::OBJECT_POST->value] = \PHRETS\Parsers\PostObject\OneEight::class;
             $this->classes[ParserType::UPDATE->value] = \PHRETS\Parsers\Update\OneEight::class;
diff --git a/src/Versions/RETSVersion.php b/src/Versions/RETSVersion.php
deleted file mode 100644
index 7652bf4..0000000
--- a/src/Versions/RETSVersion.php
+++ /dev/null
@@ -1,110 +0,0 @@
-<?php
-
-namespace PHRETS\Versions;
-
-use PHRETS\Exceptions\InvalidRETSVersion;
-
-class RETSVersion implements \Stringable
-{
-    public const VERSION_1_5 = '1.5';
-    public const VERSION_1_7 = '1.7';
-    public const VERSION_1_7_1 = '1.7.1';
-    public const VERSION_1_7_2 = '1.7.2';
-    public const VERSION_1_8 = '1.8';
-
-    protected string $number;
-
-    private const VALID_VERSIONS = [
-        self::VERSION_1_5,
-        self::VERSION_1_7,
-        self::VERSION_1_7_1,
-        self::VERSION_1_7_2,
-        self::VERSION_1_8,
-    ];
-
-    /**
-     * @param string $version
-     *
-     * @throws \PHRETS\Exceptions\InvalidRETSVersion
-     */
-    public function setVersion(string $version): self
-    {
-        $this->number = str_replace('RETS/', '', $version);
-        if (!in_array($this->number, self::VALID_VERSIONS)) {
-            throw new InvalidRETSVersion("RETS version '{$version}' given is not understood");
-        }
-
-        return $this;
-    }
-
-    public function getVersion(): string
-    {
-        return $this->number;
-    }
-
-    public function asHeader(): string
-    {
-        return 'RETS/' . $this->number;
-    }
-
-    public function is1_5(): bool
-    {
-        return $this->number == self::VERSION_1_5;
-    }
-
-    public function is1_7(): bool
-    {
-        return $this->number == self::VERSION_1_7;
-    }
-
-    public function is1_7_2(): bool
-    {
-        return $this->number == self::VERSION_1_7_2;
-    }
-
-    public function is1_8(): bool
-    {
-        return $this->number == self::VERSION_1_8;
-    }
-
-    /**
-     * @param string $version
-     */
-    public function isAtLeast(string $version): bool
-    {
-        return version_compare($this->number, $version) >= 0;
-    }
-
-    public function isAtLeast1_5(): bool
-    {
-        return $this->isAtLeast(self::VERSION_1_5);
-    }
-
-    public function isAtLeast1_7(): bool
-    {
-        return $this->isAtLeast(self::VERSION_1_7);
-    }
-
-    public function isAtLeast1_7_2(): bool
-    {
-        return $this->isAtLeast(self::VERSION_1_7_2);
-    }
-
-    public function isAtLeast1_8(): bool
-    {
-        return $this->isAtLeast(self::VERSION_1_8);
-    }
-
-    /**
-     * @return list<string>
-     */
-    public function getValidVersions(): array
-    {
-        return self::VALID_VERSIONS;
-    }
-
-    public function __toString(): string
-    {
-        return $this->asHeader();
-    }
-}
diff --git a/tests/ConfigurationTest.php b/tests/ConfigurationTest.php
index 65a9b6e..75b3e5d 100644
--- a/tests/ConfigurationTest.php
+++ b/tests/ConfigurationTest.php
@@ -5,6 +5,7 @@
 use PHPUnit\Framework\Attributes\Test;
 use PHPUnit\Framework\TestCase;
 use PHRETS\Configuration;
+use PHRETS\Enums\RETSVersion;
 use PHRETS\Session;
 use PHRETS\Strategies\SimpleStrategy;
 
@@ -48,15 +49,14 @@ public function itComplainsAboutBadConfig(): void
     public function itLoadsDefaultRetsVersion(): void
     {
         $config = new Configuration();
-        $this->assertTrue($config->getRetsVersion()->is1_5());
+        $this->assertSame(RETSVersion::VERSION_1_5, $config->getRetsVersion());
     }
 
     #[Test]
     public function itHandlesVersionsCorrectly(): void
     {
-        $config = new Configuration();
-        $config->setRetsVersion('1.7.2');
-        $this->assertTrue($config->getRetsVersion()->is1_7_2());
+        $config = new Configuration(version: RETSVersion::VERSION_1_7_2);
+        $this->assertSame(RETSVersion::VERSION_1_7_2, $config->getRetsVersion());
     }
 
     #[Test]
@@ -103,11 +103,10 @@ public function itAllowsOverridingTheStrategy(): void
     #[Test]
     public function itGeneratesUserAgentAuthHashesCorrectly(): void
     {
-        $c = new Configuration();
+        $c = new Configuration(version: RETSVersion::VERSION_1_7_2);
         $c->setLoginUrl('http://www.reso.org/login')
             ->setUserAgent('PHRETS/2.0')
-            ->setUserAgentPassword('12345')
-            ->setRetsVersion('1.7.2');
+            ->setUserAgentPassword('12345');
 
         $s = new Session($c);
         $this->assertSame('123c96e02e514da469db6bc61ab998dc', $c->userAgentDigestHash($s));
diff --git a/tests/Integration/BaseIntegration.php b/tests/Integration/BaseIntegration.php
index 207c110..39e22ed 100644
--- a/tests/Integration/BaseIntegration.php
+++ b/tests/Integration/BaseIntegration.php
@@ -6,6 +6,7 @@
 use GuzzleHttp\HandlerStack;
 use PHPUnit\Framework\TestCase;
 use PHRETS\Configuration;
+use PHRETS\Enums\RETSVersion;
 use PHRETS\Session;
 use Psr\Http\Message\RequestInterface;
 
@@ -31,11 +32,10 @@ class BaseIntegration extends TestCase
     public function setUp(): void
     {
         $this->path = __DIR__ . '/Fixtures/Http';
-        $config = new Configuration();
+        $config = new Configuration(version: RETSVersion::VERSION_1_7_2);
         $config->setLoginUrl('http://retsgw.flexmls.com/rets2_1/Login')
                 ->setUsername(getenv('PHRETS_TESTING_USERNAME'))
-                ->setPassword(getenv('PHRETS_TESTING_PASSWORD'))
-                ->setRetsVersion('1.7.2');
+                ->setPassword(getenv('PHRETS_TESTING_PASSWORD'));
 
         $this->session = $this->createSession($config);
         $this->session->Login();
diff --git a/tests/Integration/GetMetadataIntegrationTest.php b/tests/Integration/GetMetadataIntegrationTest.php
index d80cef9..d0b0195 100644
--- a/tests/Integration/GetMetadataIntegrationTest.php
+++ b/tests/Integration/GetMetadataIntegrationTest.php
@@ -3,6 +3,8 @@
 
 use PHPUnit\Framework\Attributes\Test;
 use PHRETS\Arr;
+use PHRETS\Configuration;
+use PHRETS\Enums\RETSVersion;
 
 class GetMetadataIntegrationTest extends BaseIntegration
 {
@@ -20,11 +22,10 @@ public function itGetsSystemData(): void
     #[Test]
     public function itGetsSystemDataFor15(): void
     {
-        $config = new \PHRETS\Configuration();
+        $config = new Configuration(version: RETSVersion::VERSION_1_5);
         $config->setLoginUrl('http://retsgw.flexmls.com/rets2_1/Login')
                 ->setUsername(getenv('PHRETS_TESTING_USERNAME'))
-                ->setPassword(getenv('PHRETS_TESTING_PASSWORD'))
-                ->setRetsVersion('1.5');
+                ->setPassword(getenv('PHRETS_TESTING_PASSWORD'));
 
         $session = $this->createSession($config);
         $session->Login();
@@ -228,11 +229,10 @@ public function itGetsRelatedLookupValues(): void
     #[Test]
     public function itRecoversFromBadLookuptypeTag(): void
     {
-        $config = new \PHRETS\Configuration();
+        $config = new Configuration(version: RETSVersion::VERSION_1_5);
         $config->setLoginUrl('http://retsgw.flexmls.com/lookup/rets2_1/Login')
                 ->setUsername(getenv('PHRETS_TESTING_USERNAME'))
-                ->setPassword(getenv('PHRETS_TESTING_PASSWORD'))
-                ->setRetsVersion('1.5');
+                ->setPassword(getenv('PHRETS_TESTING_PASSWORD'));
 
         $session = $this->createSession($config);
         $session->Login();
@@ -244,11 +244,10 @@ public function itRecoversFromBadLookuptypeTag(): void
     #[Test]
     public function itHandlesIncompleteObjectMetadataCorrectly(): void
     {
-        $config = new \PHRETS\Configuration();
+        $config = new \PHRETS\Configuration(version: RETSVersion::VERSION_1_5);
         $config->setLoginUrl('http://retsgw.flexmls.com/rets2_1/Login')
             ->setUsername(getenv('PHRETS_TESTING_USERNAME'))
-            ->setPassword(getenv('PHRETS_TESTING_PASSWORD'))
-            ->setRetsVersion('1.5');
+            ->setPassword(getenv('PHRETS_TESTING_PASSWORD'));
 
         $session = $this->createSession($config);
         $session->Login();
diff --git a/tests/Integration/SessionIntegrationTest.php b/tests/Integration/SessionIntegrationTest.php
index c48e5de..72e3a55 100644
--- a/tests/Integration/SessionIntegrationTest.php
+++ b/tests/Integration/SessionIntegrationTest.php
@@ -5,6 +5,7 @@
 use GuzzleHttp\Middleware;
 use PHPUnit\Framework\Attributes\Test;
 use PHRETS\Configuration;
+use PHRETS\Enums\RETSVersion;
 use PHRETS\Session;
 
 class SessionIntegrationTest extends BaseIntegration
@@ -53,13 +54,12 @@ public function itDisconnects(): void
     #[Test]
     public function itRequestsTheServersActionTransaction(): void
     {
-        $config = new \PHRETS\Configuration();
+        $config = new \PHRETS\Configuration(version: RETSVersion::VERSION_1_7_2);
 
         // this endpoint doesn't actually exist, but the response is mocked, so...
         $config->setLoginUrl('http://retsgw.flexmls.com/action/rets2_1/Login')
                 ->setUsername(getenv('PHRETS_TESTING_USERNAME'))
-                ->setPassword(getenv('PHRETS_TESTING_PASSWORD'))
-                ->setRetsVersion('1.7.2');
+                ->setPassword(getenv('PHRETS_TESTING_PASSWORD'));
 
         $session = $this->createSession($config);
         $bulletin = $session->Login();
@@ -70,13 +70,12 @@ public function itRequestsTheServersActionTransaction(): void
     #[Test]
     public function itUsesHttpPostMethodWhenDesired(): void
     {
-        $config = new \PHRETS\Configuration();
+        $config = new \PHRETS\Configuration(version: RETSVersion::VERSION_1_7_2);
 
         // this endpoint doesn't actually exist, but the response is mocked, so...
         $config->setLoginUrl('http://retsgw.flexmls.com/rets2_1/Login')
                 ->setUsername(getenv('PHRETS_TESTING_USERNAME'))
                 ->setPassword(getenv('PHRETS_TESTING_PASSWORD'))
-                ->setRetsVersion('1.7.2')
                 ->setOption('use_post_method', true);
 
         $session = $this->createSession($config);
@@ -103,15 +102,13 @@ public function itTracksAGivenSessionId(): void
     #[Test]
     public function itDetectsWhenToUseUserAgentAuthentication(): void
     {
-        $config = new Configuration();
+        $config = new Configuration(version: RETSVersion::VERSION_1_7_2);
 
         $config->setLoginUrl('http://retsgw.flexmls.com/rets2_1/Login')
                 ->setUsername(getenv('PHRETS_TESTING_USERNAME'))
                 ->setPassword(getenv('PHRETS_TESTING_PASSWORD'))
                 ->setUserAgent('PHRETS/2.0')
-                ->setUserAgentPassword('bogus_password')
-                ->setRetsVersion('1.7.2');
-
+                ->setUserAgentPassword('bogus_password');
 
         $handler = $this->createHandler();
         $session = new Session($config, new Client(['handler' => $handler]));
@@ -136,13 +133,12 @@ public function itDetectsWhenToUseUserAgentAuthentication(): void
     public function itDoesntAllowRequestsToUnsupportedCapabilities(): void
     {
         $this->expectException(\PHRETS\Exceptions\CapabilityUnavailable::class);
-        $config = new \PHRETS\Configuration();
+        $config = new Configuration(version: RETSVersion::VERSION_1_7_2);
 
         // fake, mocked endpoint
         $config->setLoginUrl('http://retsgw.flexmls.com/limited/rets2_1/Login')
                 ->setUsername(getenv('PHRETS_TESTING_USERNAME'))
-                ->setPassword(getenv('PHRETS_TESTING_PASSWORD'))
-                ->setRetsVersion('1.7.2');
+                ->setPassword(getenv('PHRETS_TESTING_PASSWORD'));
 
         $session = $this->createSession($config);
         $session->Login();
diff --git a/tests/Strategies/SimpleStrategyTest.php b/tests/Strategies/SimpleStrategyTest.php
index a875537..59183b1 100644
--- a/tests/Strategies/SimpleStrategyTest.php
+++ b/tests/Strategies/SimpleStrategyTest.php
@@ -4,6 +4,7 @@
 use PHPUnit\Framework\Attributes\Test;
 use PHPUnit\Framework\TestCase;
 use PHRETS\Configuration;
+use PHRETS\Enums\RETSVersion;
 use PHRETS\Parsers\ParserType;
 use PHRETS\Strategies\SimpleStrategy;
 
@@ -16,18 +17,17 @@ public function itProvidesDefaults(): void
         $strategy = new SimpleStrategy();
         $strategy->initialize($config);
 
-        $this->assertInstanceOf('\PHRETS\Parsers\Login\OneFive', $strategy->provide(ParserType::LOGIN));
+        $this->assertInstanceOf(\PHRETS\Parsers\Login\OneFive::class, $strategy->provide(ParserType::LOGIN));
     }
 
     #[Test]
     public function itProvidesA18LoginParser(): void
     {
-        $config = new Configuration();
-        $config->setRetsVersion('1.8');
+        $config = new Configuration(version: RETSVersion::VERSION_1_8);
         $strategy = new SimpleStrategy();
         $strategy->initialize($config);
 
-        $this->assertInstanceOf('\PHRETS\Parsers\Login\OneEight', $strategy->provide(ParserType::LOGIN));
+        $this->assertInstanceOf(\PHRETS\Parsers\Login\OneEight::class, $strategy->provide(ParserType::LOGIN));
     }
 
     #[Test]
diff --git a/tests/Versions/RETSVersionTest.php b/tests/Versions/RETSVersionTest.php
index 678cb60..62f7a5e 100644
--- a/tests/Versions/RETSVersionTest.php
+++ b/tests/Versions/RETSVersionTest.php
@@ -3,105 +3,55 @@
 
 use PHPUnit\Framework\Attributes\Test;
 use PHPUnit\Framework\TestCase;
-use PHRETS\Versions\RETSVersion;
+use PHRETS\Enums\RETSVersion;
 
 class RETSVersionTest extends TestCase
 {
     #[Test]
     public function itLoads(): void
     {
-        $this->assertSame('1.7.2', (new RETSVersion())->setVersion('1.7.2')->getVersion());
-    }
-
-    #[Test]
-    public function itCleans(): void
-    {
-        $this->assertSame('1.7.2', (new RETSVersion())->setVersion('RETS/1.7.2')->getVersion());
+        $this->assertSame('1.7.2', RETSVersion::VERSION_1_7_2->value);
     }
 
     #[Test]
     public function itMakesTheHeader(): void
     {
-        $this->assertSame('RETS/1.7.2', (new RETSVersion())->setVersion('1.7.2')->asHeader());
+        $this->assertSame('RETS/1.7.2', RETSVersion::VERSION_1_7_2->asHeader());
     }
 
     #[Test]
     public function itIs15(): void
     {
-        $v = new RETSVersion();
-        $v->setVersion('RETS/1.5');
-
-        $this->assertTrue($v->is1_5());
-        $this->assertTrue($v->isAtLeast1_5());
+        $this->assertTrue(RETSVersion::VERSION_1_5->isAtLeast(RETSVersion::VERSION_1_5));
     }
 
     #[Test]
     public function itIs17(): void
     {
-        $v = new RETSVersion();
-        $v->setVersion('RETS/1.7');
+        $v = RETSVersion::VERSION_1_7;
 
-        $this->assertTrue($v->is1_7());
-        $this->assertFalse($v->is1_5());
-        $this->assertFalse($v->is1_7_2());
-        $this->assertTrue($v->isAtLeast1_7());
-        $this->assertFalse($v->isAtLeast1_7_2());
+        $this->assertTrue($v->isAtLeast(RETSVersion::VERSION_1_7));
+        $this->assertFalse($v->isAtLeast(RETSVersion::VERSION_1_7_2));
     }
 
     #[Test]
     public function itIs172(): void
     {
-        $v = new RETSVersion();
-        $v->setVersion('RETS/1.7.2');
+        $v = RETSVersion::VERSION_1_7_2;
 
-        $this->assertFalse($v->is1_7());
-        $this->assertFalse($v->is1_5());
-        $this->assertTrue($v->is1_7_2());
-        $this->assertTrue($v->isAtLeast1_7());
-        $this->assertTrue($v->isAtLeast1_7_2());
-        $this->assertFalse($v->isAtLeast1_8());
+        $this->assertTrue($v->isAtLeast(RETSVersion::VERSION_1_7));
+        $this->assertTrue($v->isAtLeast(RETSVersion::VERSION_1_7_2));
+        $this->assertFalse($v->isAtLeast(RETSVersion::VERSION_1_8));
     }
 
     #[Test]
     public function itIs18(): void
     {
-        $v = new RETSVersion();
-        $v->setVersion('RETS/1.8');
-
-        $this->assertTrue($v->is1_8());
-        $this->assertFalse($v->is1_7());
-        $this->assertFalse($v->is1_5());
-        $this->assertFalse($v->is1_7_2());
-        $this->assertTrue($v->isAtLeast1_7());
-        $this->assertTrue($v->isAtLeast1_7_2());
-        $this->assertTrue($v->isAtLeast1_8());
-    }
-
-    #[Test]
-    public function itCompares(): void
-    {
-        $v = new RETSVersion();
-        $v->setVersion('RETS/1.8');
-
-        $this->assertTrue($v->isAtLeast('1.5'));
-        $this->assertTrue($v->isAtLeast('1.7'));
-        $this->assertTrue($v->isAtLeast('1.7.2'));
-    }
-
-    #[Test]
-    public function itFailsBadVersions(): void
-    {
-        $this->expectException(\PHRETS\Exceptions\InvalidRETSVersion::class);
-        $v = new RETSVersion();
-        $v->setVersion('2.0');
-    }
-
-    #[Test]
-    public function itConvertsToString(): void
-    {
-        $v = new RETSVersion();
-        $v->setVersion('1.7.2');
+        $v = RETSVersion::VERSION_1_8;
 
-        $this->assertSame('RETS/1.7.2', (string) $v);
+        $this->assertTrue($v->isAtLeast(RETSVersion::VERSION_1_5));
+        $this->assertTrue($v->isAtLeast(RETSVersion::VERSION_1_7));
+        $this->assertTrue($v->isAtLeast(RETSVersion::VERSION_1_7_2));
+        $this->assertTrue($v->isAtLeast(RETSVersion::VERSION_1_8));
     }
 }