diff --git a/src/test/java/de/rwu/easydrop/exception/InvalidCatalogueExceptionTest.java b/src/test/java/de/rwu/easydrop/exception/InvalidCatalogueExceptionTest.java
new file mode 100644
index 0000000..684bc57
--- /dev/null
+++ b/src/test/java/de/rwu/easydrop/exception/InvalidCatalogueExceptionTest.java
@@ -0,0 +1,33 @@
+package de.rwu.easydrop.exception;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+class InvalidCatalogueExceptionTest {
+
+    @Test
+    void testConstructorWithMessage_ExceptionWithMessageCreated() {
+        // Arrange
+        String message = "Invalid catalogue";
+
+        // Act
+        InvalidCatalogueException exception = new InvalidCatalogueException(message);
+
+        // Assert
+        Assertions.assertEquals(message, exception.getMessage());
+    }
+
+    @Test
+    void testConstructorWithMessageAndCause_ExceptionWithMessageAndCauseCreated() {
+        // Arrange
+        String message = "Invalid catalogue";
+        Throwable cause = new RuntimeException("Cause exception");
+
+        // Act
+        InvalidCatalogueException exception = new InvalidCatalogueException(message, cause);
+
+        // Assert
+        Assertions.assertEquals(message, exception.getMessage());
+        Assertions.assertEquals(cause, exception.getCause());
+    }
+}
diff --git a/src/test/java/de/rwu/easydrop/service/processing/OrderManagerTest.java b/src/test/java/de/rwu/easydrop/service/processing/OrderManagerTest.java
index a83fdc8..2ffb76a 100644
--- a/src/test/java/de/rwu/easydrop/service/processing/OrderManagerTest.java
+++ b/src/test/java/de/rwu/easydrop/service/processing/OrderManagerTest.java
@@ -1,9 +1,17 @@
 package de.rwu.easydrop.service.processing;
 
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import java.lang.reflect.Constructor;
+import java.lang.reflect.InvocationTargetException;
+import java.lang.reflect.Modifier;
 import java.util.ArrayList;
 import java.util.List;
 
-import org.junit.jupiter.api.Assertions;
 import org.junit.jupiter.api.Test;
 
 import de.rwu.easydrop.exception.InvalidCatalogueException;
@@ -13,15 +21,29 @@ import de.rwu.easydrop.model.ProductPair;
 
 class OrderManagerTest {
 
+    @Test
+    void testConstructorIsPrivate()
+            throws NoSuchMethodException, IllegalAccessException, InvocationTargetException, InstantiationException {
+        // Check for private constructor
+        Constructor<OrderManager> constructor = OrderManager.class.getDeclaredConstructor();
+        assertTrue(Modifier.isPrivate(constructor.getModifiers()));
+
+        // Make sure exception is thrown when instantiating
+        constructor.setAccessible(true);
+        assertThrows(InvocationTargetException.class, () -> {
+            constructor.newInstance();
+        });
+    }
+
     @Test
     void testCreateOrders_ValidCatalogues_OrdersCreated() {
         // Arrange
         List<ProductCatalogue> catalogues = createSampleCatalogues();
 
         // Act
-        OrderManager.createOrders(catalogues);
-
-        // No assertions, just checking if the orders are created successfully
+        assertDoesNotThrow(() -> {
+            OrderManager.createOrders(catalogues);
+        });
     }
 
     @Test
@@ -33,11 +55,11 @@ class OrderManagerTest {
         ProductPair pair = OrderManager.getHighestMarginProducts(catalogue);
 
         // Assert
-        Assertions.assertNotNull(pair);
-        Assertions.assertNotNull(pair.getProduct1());
-        Assertions.assertNotNull(pair.getProduct2());
-        Assertions.assertEquals("Product1", pair.getProduct1().getProductId());
-        Assertions.assertEquals("Product3", pair.getProduct2().getProductId());
+        assertNotNull(pair);
+        assertNotNull(pair.getProduct1());
+        assertNotNull(pair.getProduct2());
+        assertEquals("Product2", pair.getProduct1().getProductId());
+        assertEquals("Product3", pair.getProduct2().getProductId());
     }
 
     @Test
@@ -48,8 +70,25 @@ class OrderManagerTest {
         // The catalogue has only one product, which is invalid
 
         // Act & Assert
-        Assertions.assertThrows(InvalidCatalogueException.class,
+        Exception e = assertThrows(InvalidCatalogueException.class,
                 () -> OrderManager.getHighestMarginProducts(catalogue));
+
+        assertEquals("Product Catalogue holds less than 2 products!", e.getMessage());
+    }
+
+    @Test
+    void testGetHighestMarginProducts_InvalidCatalogue_NoMargin() {
+        // Arrange
+        ProductCatalogue catalogue = new ProductCatalogue("Catalogue1", "Sample catalogue");
+        catalogue.addProduct(new Product());
+        catalogue.addProduct(new Product());
+        // The catalogue has only one product, which is invalid
+
+        // Act & Assert
+        Exception e = assertThrows(InvalidCatalogueException.class,
+                () -> OrderManager.getHighestMarginProducts(catalogue));
+
+        assertEquals("Price margin is zero!", e.getMessage());
     }
 
     private List<ProductCatalogue> createSampleCatalogues() {
@@ -80,7 +119,7 @@ class OrderManagerTest {
         catalogue.addProduct(product1);
         Product product2 = new Product();
         product2.setProductId("Product2");
-        product2.setCurrentPrice(2.34);
+        product2.setCurrentPrice(0.89);
         catalogue.addProduct(product2);
         Product product3 = new Product();
         product3.setProductId("Product3");