added ParameterizedTest for offer validator

src/main/java/de/rwu/easydrop/service/validation/OfferValidator.java

@@ -28,6 +28,9 @@ public final class OfferValidator {
             if (offer.getOfferId().equals("")) {
                 throw new InvalidOfferException("Offer ID cannot be empty");
             }
+            if (offer.getLastUpdate().equals("")) {
+                throw new InvalidOfferException("LastUpdate cannot be empty");
+            }
         } catch (NullPointerException e) {
             throw new InvalidOfferException("Required information is missing in the offer", e);
         }

src/test/java/de/rwu/easydrop/service/validation/OfferValidatorTest.java

@@ -3,6 +3,8 @@ package de.rwu.easydrop.service.validation;
 import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
 import static org.junit.jupiter.api.Assertions.assertThrows;
 
+import java.util.stream.Stream;
+
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.MethodSource;
@@ -25,11 +27,31 @@ public class OfferValidatorTest {
     }
 
     @ParameterizedTest
-    @MethodSource("invalidOffer")
+    @MethodSource("invalidOfferProvider")
     void validate_InvalidOffer_ThrowsInvalidOfferException(Offer offer) {
         // Act and Assert
         assertThrows(InvalidOfferException.class, () -> OfferValidator.validate(offer));
-    }
-
+
+    }
+
+    static Stream<Offer> invalidOfferProvider() {
+        return Stream.of(
+            createOfferWithEmptylastUpdate(), 
+            createOfferWithEmptyId());
+    }
+
+    private static Offer createOfferWithEmptylastUpdate() {
+        Offer offer = new Offer();
+        offer.setOfferId("3729798");
+        offer.setLastUpdate("");
+        return offer;
+    }
+
+    private static Offer createOfferWithEmptyId() {
+        Offer offer = new Offer();
+        offer.setOfferId("");
+        offer.setLastUpdate("8798476");
+        return offer;
+    }
     
 }