diff --git a/src/Mapping/Factory/MetadataFactory.php b/src/Mapping/Factory/MetadataFactory.php
index f6c8b64..56e12de 100644
--- a/src/Mapping/Factory/MetadataFactory.php
+++ b/src/Mapping/Factory/MetadataFactory.php
@@ -60,7 +60,7 @@ public function getMetadataFor($value): ClassMetadata
         }
 
         if (!class_exists($className)) {
-            throw new NoSuchMetadataException(sprintf('The class or interface "%s" does not exist.', $className));
+            throw new NoSuchMetadataException(sprintf('The class "%s" does not exist.', $className));
         }
 
         $metadata = new ClassMetadata($className);
@@ -77,10 +77,6 @@ public function getMetadataFor($value): ClassMetadata
 
     private function mergeLoaders(ClassMetadata $metadata): void
     {
-        if ($metadata->getReflectionClass()->isInterface()) {
-            return;
-        }
-
         // Include loaders from the parent class
         if ($parent = $metadata->getReflectionClass()->getParentClass()) {
             $metadata->mergePropertyLoaders($this->getMetadataFor($parent->name));
diff --git a/tests/Mapping/Factory/MetadataFactoryTest.php b/tests/Mapping/Factory/MetadataFactoryTest.php
index a9c94da..4327748 100644
--- a/tests/Mapping/Factory/MetadataFactoryTest.php
+++ b/tests/Mapping/Factory/MetadataFactoryTest.php
@@ -5,8 +5,10 @@
 
 
 use Doctrine\Common\Annotations\AnnotationReader;
+use Guennichi\PropertyLoader\Exception\NoSuchMetadataException;
 use Guennichi\PropertyLoader\Mapping\Factory\MetadataFactory;
 use Guennichi\PropertyLoader\Mapping\Loader\AnnotationLoader;
+use Guennichi\PropertyLoader\Mapping\Loader\LoaderInterface;
 use Guennichi\PropertyLoader\Tests\Fixtures\Child;
 use PHPUnit\Framework\TestCase;
 
@@ -20,4 +22,50 @@ public function testCreateMetadataWithParentClasses(): void
 
         $this->assertCount(2, $metadata->getTargetProperties());
     }
+
+    public function testGetSameMetadataObjectIfCalledMoreThanOne(): void
+    {
+        $loader = new AnnotationLoader(new AnnotationReader());
+        $factory = new MetadataFactory($loader);
+
+        $meta1 = $factory->getMetadataFor(Foo::class);
+        $meta2 = $factory->getMetadataFor(Foo::class);
+
+        $this->assertTrue($meta1 === $meta2);
+    }
+
+    public function testThrowExceptionIfNotValidClassnameOrObject(): void
+    {
+        $loader = new AnnotationLoader(new AnnotationReader());
+        $factory = new MetadataFactory($loader);
+
+        $exceptions = [];
+
+        try {
+            $factory->getMetadataFor(15);
+        } catch (NoSuchMetadataException $e) {
+            $exceptions[] = $e;
+        }
+
+        try {
+            $factory->getMetadataFor('foo');
+        } catch (NoSuchMetadataException $e) {
+            $exceptions[] = $e;
+        }
+
+        $this->assertCount(2, $exceptions);
+
+        $this->assertSame('Cannot create metadata for non-objects. Got: "int"', $exceptions[0]->getMessage());
+        $this->assertSame('The class "foo" does not exist.', $exceptions[1]->getMessage());
+    }
+}
+
+class Foo
+{
+
+}
+
+interface FooInterface
+{
+
 }
diff --git a/tests/Mapping/Loader/StaticMethodLoaderTest.php b/tests/Mapping/Loader/StaticMethodLoaderTest.php
index 54731f3..9008ac9 100644
--- a/tests/Mapping/Loader/StaticMethodLoaderTest.php
+++ b/tests/Mapping/Loader/StaticMethodLoaderTest.php
@@ -4,6 +4,7 @@
 namespace Guennichi\PropertyLoader\Tests\Mapping\Loader;
 
 
+use Guennichi\PropertyLoader\Exception\MappingException;
 use Guennichi\PropertyLoader\Mapping\ClassMetadata;
 use Guennichi\PropertyLoader\Mapping\Loader\StaticMethodLoader;
 use Guennichi\PropertyLoader\Tests\Fixtures\Loaders\Gmail;
@@ -19,7 +20,7 @@ public function testLoadClassMetadataReturnsTrueIfSuccessful(): void
         $this->assertTrue($loader->loadClassMetadata($metadata));
     }
 
-    public function testLoadClassMetadataReturnsFalseIfNotSuccessful()
+    public function testLoadClassMetadataReturnsFalseIfNotSuccessful(): void
     {
         $loader = new StaticMethodLoader('loadMetadata');
         $metadata = new ClassMetadata('\stdClass');
@@ -27,7 +28,7 @@ public function testLoadClassMetadataReturnsFalseIfNotSuccessful()
         $this->assertFalse($loader->loadClassMetadata($metadata));
     }
 
-    public function testLoadClassMetadata()
+    public function testLoadClassMetadata(): void
     {
         $loader = new StaticMethodLoader('loadMetadata');
         $metadata = new ClassMetadata(StaticLoaderEntity::class);
@@ -38,7 +39,7 @@ public function testLoadClassMetadata()
     }
 
 
-    public function testLoadClassMetadataDoesNotRepeatLoadWithParentClasses()
+    public function testLoadClassMetadataDoesNotRepeatLoadWithParentClasses(): void
     {
         $loader = new StaticMethodLoader('loadMetadata');
         $metadata = new ClassMetadata(StaticLoaderDocument::class);
@@ -51,7 +52,7 @@ public function testLoadClassMetadataDoesNotRepeatLoadWithParentClasses()
         $this->assertCount(1, $metadata->getTargetProperties());
     }
 
-    public function testLoadClassMetadataIgnoresInterfaces()
+    public function testLoadClassMetadataIgnoresInterfaces(): void
     {
         $loader = new StaticMethodLoader('loadMetadata');
         $metadata = new ClassMetadata(StaticLoaderInterface::class);
@@ -61,7 +62,7 @@ public function testLoadClassMetadataIgnoresInterfaces()
         $this->assertCount(0, $metadata->getTargetProperties());
     }
 
-    public function testLoadClassMetadataInAbstractClasses()
+    public function testLoadClassMetadataInAbstractClasses(): void
     {
         $loader = new StaticMethodLoader('loadMetadata');
         $metadata = new ClassMetadata(AbstractStaticLoader::class);
@@ -70,6 +71,25 @@ public function testLoadClassMetadataInAbstractClasses()
 
         $this->assertCount(1, $metadata->getTargetProperties());
     }
+
+    public function testLoadClassMetadataInNonStaticMethods(): void
+    {
+        $loader = new StaticMethodLoader('loadMetadata');
+        $metadata = new ClassMetadata(NonStaticLoaderEntity::class);
+
+        $this->expectException(MappingException::class);
+        $this->expectExceptionMessage('The method "Guennichi\PropertyLoader\Tests\Mapping\Loader\NonStaticLoaderEntity::loadMetadata()" should be static.');
+
+        $loader->loadClassMetadata($metadata);
+    }
+
+    public function testLoadClassMetadataInAbstractStaticMethods(): void
+    {
+        $loader = new StaticMethodLoader('loadMetadata');
+        $metadata = new ClassMetadata(AbstractMethodStaticLoader::class);
+
+        $this->assertFalse($loader->loadClassMetadata($metadata));
+    }
 }
 
 interface StaticLoaderInterface
@@ -79,17 +99,32 @@ public static function loadMetadata(ClassMetadata $metadata);
 
 abstract class AbstractStaticLoader
 {
-    public static function loadMetadata(ClassMetadata $metadata)
+    public static function loadMetadata(ClassMetadata $metadata): void
     {
         $metadata->addPropertyLoader('foo', new Gmail());
     }
 }
 
+class NonStaticLoaderEntity
+{
+    public static ?ClassMetadata $invokedWith = null;
+
+    public function loadMetadata(ClassMetadata $metadata): void
+    {
+        self::$invokedWith = $metadata;
+    }
+}
+
+abstract class AbstractMethodStaticLoader
+{
+    public abstract static function loadMetadata(ClassMetadata $metadata): void;
+}
+
 class StaticLoaderEntity
 {
     public static ?ClassMetadata $invokedWith = null;
 
-    public static function loadMetadata(ClassMetadata $metadata)
+    public static function loadMetadata(ClassMetadata $metadata): void
     {
         self::$invokedWith = $metadata;
     }