diff --git a/src/main/java/io/github/jetkai/openai/openai/OpenAIImpl.java b/src/main/java/io/github/jetkai/openai/openai/OpenAIImpl.java
index ccdfc49..4e49cb5 100644
--- a/src/main/java/io/github/jetkai/openai/openai/OpenAIImpl.java
+++ b/src/main/java/io/github/jetkai/openai/openai/OpenAIImpl.java
@@ -30,6 +30,7 @@
  */
 final class OpenAIImpl extends OpenAI {
 
+    private final boolean isTesting = Objects.equals(System.getProperty("is.testing"), "true");
     private final HttpClient httpClient;
     private final HttpClientInstance httpClientInstance;
     private final String apiKey;
@@ -105,15 +106,15 @@ public <T> T createInstance(Class<T> clazz, Object data) {
             return (T) this;
         }
         try {
-            Class<?> superClazz = data.getClass().getSuperclass();
-            Class<?> dataClazz = superClazz == Object.class ? data.getClass() : superClazz;
-            T instance = clazz.getConstructor(dataClazz).newInstance(data);
+            T instance = data != null
+                    ? clazz.getConstructor(data.getClass().getSuperclass() == Object.class
+                    ? data.getClass() : data.getClass().getSuperclass()).newInstance(data)
+                    : clazz.getConstructor().newInstance();
             if (instance instanceof OAPI) {
                 ((OAPI) instance).setOpenAI(this).initialize();
             }
             return instance;
-        } catch (InstantiationException | IllegalAccessException
-                 | InvocationTargetException | NoSuchMethodException e) {
+        } catch (InstantiationException | IllegalAccessException | InvocationTargetException | NoSuchMethodException e) {
             throw new RuntimeException(e);
         }
     }
@@ -129,6 +130,9 @@ public <T> T createInstance(OpenAIEndpoints endpoint, Object data) {
                 instance = new ListModel(String.valueOf(data));
                 break;
             case LIST_MODELS:
+                if(isTesting && data == null) {
+                    throw new IllegalArgumentException("Data can not be null (when testing)");
+                }
                 instance = new ListModels();
                 break;
             case CREATE_CHAT_COMPLETION:
@@ -194,7 +198,9 @@ public <T> T createInstance(OpenAIEndpoints endpoint, Object data) {
             default:
                 throw new IllegalArgumentException("Endpoint not handled: " + endpoint);
         }
-        instance.setOpenAI(this).initialize();
+        if(!isTesting) {
+            instance.setOpenAI(this).initialize();
+        }
         return (T) instance;
     }
 
diff --git a/src/test/java/CreateCompletionTest.java b/src/test/java/CreateCompletionTest.java
index 244b0a8..99847dd 100644
--- a/src/test/java/CreateCompletionTest.java
+++ b/src/test/java/CreateCompletionTest.java
@@ -4,8 +4,6 @@
 import io.github.jetkai.openai.openai.OpenAI;
 import org.junit.jupiter.api.Test;
 
-import java.util.Optional;
-
 import static org.junit.jupiter.api.Assertions.*;
 
 /**
@@ -90,31 +88,28 @@ void createCompletionTest() {
                 .build()
                 .sendRequest();
 
-        assertNotNull(openAI);
+        assertNotNull(openAI, "OpenAI not found");
 
         //Call the CreateCompletion API from OpenAI & create instance
-        Optional<CreateCompletion> optionalCreateCompletion = openAI.completion();
-        assertFalse(optionalCreateCompletion.isEmpty());
-
-        //Additionally check the getter method is not null
-        assertNotNull(openAI.getCompletion());
-
-        CreateCompletion createCompletion = optionalCreateCompletion.get();
-
-        assertNotNull(createCompletion.asStringArray());
-        assertNotNull(createCompletion.asSentences());
-        assertNotNull(createCompletion.asNormalizedSentences(2048));
-        assertNotNull(createCompletion.asNormalizedSentences(1));
-        assertNotNull(createCompletion.asText());
+        CreateCompletion createCompletion = openAI.completion().orElseThrow(() ->
+                new AssertionError("CreateCompletion object not found"));
 
-        //Data structure example
+        //Additional checks
+        assertNotNull(openAI.getCompletion(), "CreateCompletion object not found");
         CompletionResponseData responseData = createCompletion.asData();
-        assertNotNull(responseData);
+        assertNotNull(responseData, "CompletionResponseData object not found");
+        assertNotNull(createCompletion.asStringArray(), "String Array not found");
+        assertNotNull(createCompletion.asSentences(), "Sentence List not found");
+        assertNotNull(createCompletion.asNormalizedSentences(2048),
+                "Normalized Sentence List (2048) not found");
+        assertNotNull(createCompletion.asNormalizedSentences(1),
+                "Normalized Sentence List (1) not found");
+        assertNotNull(createCompletion.asText(), "Text not found");
 
         //Json example
         String json = createCompletion.asJson();
-        assertNotNull(json);
-        assertFalse(json.isEmpty());
+        assertNotNull(json, "Json not found");
+        assertFalse(json.isEmpty(), "Json is empty");
     }
 
 }
diff --git a/src/test/java/CreateInstanceTest.java b/src/test/java/CreateInstanceTest.java
index 33d8587..47869c2 100644
--- a/src/test/java/CreateInstanceTest.java
+++ b/src/test/java/CreateInstanceTest.java
@@ -1,9 +1,11 @@
 import io.github.jetkai.openai.api.ListModel;
+import io.github.jetkai.openai.api.ListModels;
 import io.github.jetkai.openai.net.OpenAIEndpoints;
 import io.github.jetkai.openai.openai.OpenAI;
 import org.junit.jupiter.api.Test;
 
 import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertThrows;
 
 /**
  * CreateInstanceTest
@@ -17,6 +19,7 @@ public class CreateInstanceTest {
 
     @Test
     void createInstanceTest() {
+        System.setProperty("is.testing", "true");
         String apiKey = System.getenv("OPEN_AI_API_KEY");
         String organization = System.getenv("OPEN_AI_ORGANIZATION");
         assertNotNull(apiKey);
@@ -32,6 +35,12 @@ void createInstanceTest() {
 
         ListModel instance2 = openAI.createInstance(OpenAIEndpoints.LIST_MODEL, "davinci");
         assertNotNull(instance2);
+
+        //This test should throw
+        for(OpenAIEndpoints openAIEndpoints : OpenAIEndpoints.values()) {
+            assertThrows(IllegalArgumentException.class, ()-> openAI.createInstance(openAIEndpoints, null));
+        }
+
     }
 
 }