diff --git a/README.md b/README.md
index f81bd2f..9f71f65 100644
--- a/README.md
+++ b/README.md
@@ -144,7 +144,7 @@ class MyModuleServiceContainer extends ServiceContainer
     {
         if (null === $this->logger) {
             $this->logger = LoggerFactory::create(
-                $this->getParameterWithDefault(
+                $this->getParameter(
                     'ps_accounts.log_level',
                     LoggerFactory::ERROR
                 )
diff --git a/src/ServiceContainer/ServiceContainer.php b/src/ServiceContainer/ServiceContainer.php
index 9979058..2d25d2b 100644
--- a/src/ServiceContainer/ServiceContainer.php
+++ b/src/ServiceContainer/ServiceContainer.php
@@ -164,32 +164,21 @@ public function has($name)
 
     /**
      * @param string $name
+     * @param mixed $default
      *
-     * @return string
+     * @return mixed
      *
      * @throws ParameterNotFoundException
      */
-    public function getParameter($name)
+    public function getParameter($name, $default = null)
     {
         if (array_key_exists($name, $this->config)) {
             return $this->config[$name];
         }
-        throw new ParameterNotFoundException('Configuration parameter "' . $name . '" not found.');
-    }
-
-    /**
-     * @param string $name
-     * @param string $default
-     *
-     * @return string
-     */
-    public function getParameterWithDefault($name, $default)
-    {
-        if (array_key_exists($name, $this->config)) {
-            return $this->config[$name];
+        if (func_num_args() > 1) {
+            return $default;
         }
-
-        return $default;
+        throw new ParameterNotFoundException('Configuration parameter "' . $name . '" not found.');
     }
 
     /**
diff --git a/tests/src/ServiceContainer/ServiceContainerTest.php b/tests/src/ServiceContainer/ServiceContainerTest.php
index 40ee7e4..1176033 100644
--- a/tests/src/ServiceContainer/ServiceContainerTest.php
+++ b/tests/src/ServiceContainer/ServiceContainerTest.php
@@ -7,14 +7,6 @@
 use PrestaShopCorp\LightweightContainer\ServiceContainer\Exception\ServiceNotFoundException;
 use PrestaShopCorp\LightweightContainer\ServiceContainer\ServiceContainer;
 
-class TestService
-{
-    public function init()
-    {
-        // empty method
-    }
-}
-
 class ServiceContainerTest extends TestCase
 {
     /**
@@ -50,19 +42,83 @@ public function itShouldThrowParameterNotFoundExceptionIfParameterNotFound()
     /**
      * @test
      */
-    public function itShouldGetConfigurationParameter()
+    public function itShouldGetParameter()
     {
+        $this->assertTrue($this->container->hasParameter('log_level'));
         $this->assertEquals('DEBUG', $this->container->getParameter('log_level'));
     }
 
+    /**
+     * @test
+     */
+    public function itShouldGetParameterDefaultValue()
+    {
+        $default = 'foo';
+
+        $this->assertFalse($this->container->hasParameter('not_found'));
+        $this->assertEquals($default, $this->container->getParameter('not_found', $default));
+    }
+
+    /**
+     * @test
+     */
+    public function itShouldGetParameterDefaultNullValue()
+    {
+        $default = null;
+
+        $this->assertFalse($this->container->hasParameter('not_found'));
+        $this->assertEquals($default, $this->container->getParameter('not_found', $default));
+    }
+
+    /**
+     * @test
+     */
+    public function itShouldNotGetParameterDefaultValue()
+    {
+        $default = 'foo';
+
+        $this->assertTrue($this->container->hasParameter('log_level'));
+        $this->assertEquals('DEBUG', $this->container->getParameter('log_level', $default));
+    }
+
+    /**
+     * @test
+     */
+    public function itShouldSetService()
+    {
+        $service = new TestService();
+        $this->container->set(TestService::class, $service);
+
+        $this->assertTrue($this->container->has(TestService::class));
+        $this->assertSame($service, $this->container->get(TestService::class));
+    }
+
+    /**
+     * @test
+     */
+    public function itShouldReplaceService()
+    {
+        $service = new TestService();
+        $this->container->set(TestService::class, $service);
+
+        $this->assertTrue($this->container->has(TestService::class));
+        $this->assertSame($service, $this->container->get(TestService::class));
+
+        $service2 = new TestService();
+        $this->container->set(TestService::class, $service2);
+
+        $this->assertTrue($this->container->has(TestService::class));
+        $this->assertSame($service2, $this->container->get(TestService::class));
+
+        $this->assertNotSame($service, $service2);
+    }
+
     /**
      * @test
      */
     public function itShouldInstantiateServiceOnlyOnce()
     {
         $service = $this->createMock(TestService::class);
-        $service->expects($this->once())->method('init');
-
         $this->container->registerProvider(TestService::class, static function () use ($service) {
             $service->init();
 
@@ -71,9 +127,27 @@ public function itShouldInstantiateServiceOnlyOnce()
 
         $this->assertTrue($this->container->hasProvider(TestService::class));
 
-        $i = 0;
-        while ($i++ < 3) {
-            $this->assertInstanceOf(TestService::class, $this->container->get(TestService::class));
-        }
+        $service->expects($this->once())->method('init');
+
+        $instance1 = $this->container->get(TestService::class);
+        $instance2 = $this->container->get(TestService::class);
+
+        $this->assertTrue($this->container->has(TestService::class));
+
+        $this->assertInstanceOf(TestService::class, $instance1);
+        $this->assertInstanceOf(TestService::class, $instance2);
+
+        $this->assertSame($instance1, $instance2);
+    }
+
+    /**
+     * @test
+     */
+    public function itShouldInstantiateSingletonService()
+    {
+        $instance = $this->container->get(TestSingletonService::class);
+
+        $this->assertInstanceOf(TestSingletonService::class, $instance);
+        $this->assertTrue($this->container->has(TestSingletonService::class));
     }
 }
diff --git a/tests/src/ServiceContainer/TestService.php b/tests/src/ServiceContainer/TestService.php
new file mode 100644
index 0000000..0cc00f7
--- /dev/null
+++ b/tests/src/ServiceContainer/TestService.php
@@ -0,0 +1,11 @@
+<?php
+
+namespace PrestaShopCorp\LightweightContainer\Test\ServiceContainer;
+
+class TestService
+{
+    public function init()
+    {
+        // empty method
+    }
+}
diff --git a/tests/src/ServiceContainer/TestSingletonService.php b/tests/src/ServiceContainer/TestSingletonService.php
new file mode 100644
index 0000000..1bb87b9
--- /dev/null
+++ b/tests/src/ServiceContainer/TestSingletonService.php
@@ -0,0 +1,20 @@
+<?php
+
+namespace PrestaShopCorp\LightweightContainer\Test\ServiceContainer;
+
+use PrestaShopCorp\LightweightContainer\ServiceContainer\Contract\ISingletonService;
+use PrestaShopCorp\LightweightContainer\ServiceContainer\ServiceContainer;
+
+class TestSingletonService implements ISingletonService
+{
+    private static $instance;
+
+    public static function getInstance(ServiceContainer $serviceContainer)
+    {
+        if (self::$instance === null) {
+            self::$instance = new TestSingletonService();
+        }
+
+        return self::$instance;
+    }
+}