diff --git a/_config/injector.yml b/_config/injector.yml
index 2b35577..6885610 100644
--- a/_config/injector.yml
+++ b/_config/injector.yml
@@ -22,3 +22,11 @@ SilverStripe\Core\Injector\Injector:
     class: SilverStripe\EnvironmentCheck\Checks\SolrIndexCheck
   URLCheck:
     class: SilverStripe\EnvironmentCheck\Checks\URLCheck
+  EnvCheckClient:
+    factory: 'SilverStripe\EnvironmentCheck\Services\ClientFactory'
+    constructor:
+      timeout: 10.0
+
+SilverStripe\EnvironmentCheck\Checks\SessionCheck:
+    dependencies:
+      client: '%$EnvCheckClient'
diff --git a/src/Checks/SessionCheck.php b/src/Checks/SessionCheck.php
index d7779da..47a95bd 100644
--- a/src/Checks/SessionCheck.php
+++ b/src/Checks/SessionCheck.php
@@ -2,10 +2,7 @@
 
 namespace SilverStripe\EnvironmentCheck\Checks;
 
-use SilverStripe\Control\Director;
-use SilverStripe\Control\Controller;
 use Psr\Http\Message\ResponseInterface;
-use SilverStripe\Core\Config\Configurable;
 use SilverStripe\EnvironmentCheck\Traits\Fetcher;
 use SilverStripe\EnvironmentCheck\EnvironmentCheck;
 
@@ -17,16 +14,8 @@ use SilverStripe\EnvironmentCheck\EnvironmentCheck;
  */
 class SessionCheck implements EnvironmentCheck
 {
-    use Configurable;
     use Fetcher;
 
-    /**
-     * URL to check
-     *
-     * @var string
-     */
-    protected $url;
-
     /**
      * Set up check with URL
      *
@@ -35,11 +24,7 @@ class SessionCheck implements EnvironmentCheck
      */
     public function __construct($url = '')
     {
-        $this->url = $url;
-        $this->clientConfig = [
-            'base_uri' => Director::absoluteBaseURL(),
-            'timeout' => 10.0,
-        ];
+        $this->setURL($url);
     }
 
     /**
@@ -49,9 +34,9 @@ class SessionCheck implements EnvironmentCheck
      */
     public function check()
     {
-        $response = $this->fetchResponse($this->url);
+        $response = $this->client->get($this->getURL());
         $cookie = $this->getCookie($response);
-        $fullURL = Controller::join_links(Director::absoluteBaseURL(), $this->url);
+        $fullURL = $this->getURL();
 
         if ($cookie) {
             return [
diff --git a/src/Services/ClientFactory.php b/src/Services/ClientFactory.php
new file mode 100644
index 0000000..ef066f0
--- /dev/null
+++ b/src/Services/ClientFactory.php
@@ -0,0 +1,49 @@
+<?php
+
+namespace SilverStripe\EnvironmentCheck\Services;
+
+use GuzzleHttp\Client as GuzzleClient;
+use SilverStripe\Core\Injector\Factory;
+use SilverStripe\Core\Config\Configurable;
+
+/**
+ * Factory class for creating HTTP client which are injected into some env check classes. Inject via YAML,
+ * arguments for Guzzle client can be supplied using "constructor" property or set as default_config.
+ *
+ * @see SilverStripe\EnvironmentCheck\Traits\Fetcher
+ */
+class ClientFactory implements Factory
+{
+    use Configurable;
+
+    /**
+     * Default config for Guzzle client.
+     *
+     * @var array
+     */
+    private static $default_config = [];
+
+    /**
+     * Wrapper to create a Guzzle client.
+     *
+     * {@inheritdoc}
+     */
+    public function create($service, array $params = [])
+    {
+        return new GuzzleClient($this->getConfig($params));
+    }
+
+    /**
+     * Merge config provided from yaml with default config
+     *
+     * @param array $overrides
+     * @return array
+     */
+    public function getConfig(array $overrides)
+    {
+        return array_merge(
+            $this->config()->get('default_config'),
+            $overrides
+        );
+    }
+}
diff --git a/src/Traits/Fetcher.php b/src/Traits/Fetcher.php
index afba398..60dd5c3 100644
--- a/src/Traits/Fetcher.php
+++ b/src/Traits/Fetcher.php
@@ -2,45 +2,50 @@
 
 namespace SilverStripe\EnvironmentCheck\Traits;
 
-use GuzzleHttp\Client;
-use Psr\Http\Message\ResponseInterface;
+use SilverStripe\Control\Director;
 
 /**
- * Simple helper for fetching responses using Guzzle client.
+ * Simple helper for env checks which require HTTP clients.
  *
  * @package environmentcheck
  */
 trait Fetcher
 {
     /**
-     * Configuration for the Guzzle client
+     * Client for making requests, set vi Injector.
      *
-     * @var array
+     * @see SilverStripe\EnvironmentCheck\Services
+     *
+     * @var GuzzleHttp\Client
      */
-    protected $clientConfig = [];
+    public $client = null;
 
     /**
-     * Merges configuration arrays and returns the result
+     * Absolute URL for requests.
      *
-     * @param array $extraConfig
-     * @return array
+     * @var string
      */
-    private function getClientConfig(array $extraConfig = [])
+    protected $url;
+
+    /**
+     * Set URL for requests.
+     *
+     * @param string $url Relative URL
+     * @return self
+     */
+    public function setURL($url)
     {
-        return array_merge($this->clientConfig, $extraConfig);
+        $this->url = Director::absoluteURL($url);
+        return $this;
     }
 
     /**
-     * Fetch a response for a URL using Guzzle client.
+     * Getter for URL
      *
-     * @param string $url
-     * @param array|null $extraConfig Extra configuration
-     * @return ResponseInterface
+     * @return string
      */
-    public function fetchResponse(string $url, array $extraConfig = [])
+    public function getURL()
     {
-        $config = $this->getClientConfig($extraConfig);
-        $client = new Client($config);
-        return $client->get($url);
+        return $this->url;
     }
 }
diff --git a/tests/Checks/SessionCheckTest.php b/tests/Checks/SessionCheckTest.php
new file mode 100644
index 0000000..a84bcef
--- /dev/null
+++ b/tests/Checks/SessionCheckTest.php
@@ -0,0 +1,76 @@
+<?php
+
+namespace SilverStripe\EnvironmentCheck\Tests\Checks;
+
+use GuzzleHttp\Client;
+use GuzzleHttp\HandlerStack;
+use GuzzleHttp\Psr7\Response;
+use SilverStripe\Dev\SapphireTest;
+use GuzzleHttp\Handler\MockHandler;
+use SilverStripe\EnvironmentCheck\EnvironmentCheck;
+use SilverStripe\EnvironmentCheck\Checks\SessionCheck;
+
+/**
+ * Test session checks.
+ */
+class SessionCheckTest extends SapphireTest
+{
+    /**
+     * @var SilverStripe\EnvironmentCheck\Checks\SessionCheck
+     */
+    public $sessionCheck = null;
+
+    /**
+     * Create a session check for use by tests.
+     *
+     * @return void
+     */
+    protected function setUp()
+    {
+        parent::setUp();
+        $this->sessionCheck = new SessionCheck('/');
+    }
+
+    /**
+     * Env check reports error when session cookies are being set.
+     *
+     * @return void
+     */
+    public function testSessionSet()
+    {
+        // Create a mock and queue two responses.
+        $mock = new MockHandler([
+            new Response(200, ['Set-Cookie' => 'PHPSESSID:foo']),
+            new Response(200, ['Set-Cookie' => 'SECSESSID:bar'])
+        ]);
+
+        $handler = HandlerStack::create($mock);
+        $client = new Client(['handler' => $handler]);
+        $this->sessionCheck->client = $client;
+
+        // Check for PHPSESSID
+        $this->assertContains(EnvironmentCheck::ERROR, $this->sessionCheck->check());
+
+        // Check for SECSESSID
+        $this->assertContains(EnvironmentCheck::ERROR, $this->sessionCheck->check());
+    }
+
+    /**
+     * Env check responds OK when no session cookies are set in response.
+     *
+     * @return void
+     */
+    public function testSessionNotSet()
+    {
+        // Create a mock and queue two responses.
+        $mock = new MockHandler([
+            new Response(200)
+        ]);
+
+        $handler = HandlerStack::create($mock);
+        $client = new Client(['handler' => $handler]);
+        $this->sessionCheck->client = $client;
+
+        $this->assertContains(EnvironmentCheck::OK, $this->sessionCheck->check());
+    }
+}