get instance empty list

src/main/java/hs/fulda/de/ci/exam/project/Flight.java

@@ -1,5 +1,6 @@
 package hs.fulda.de.ci.exam.project;
 
+import java.util.HashSet;
 import java.util.LinkedList;
 
 public class Flight {
@@ -7,7 +8,7 @@ public class Flight {
     Airport departure;
     Airport arrival;
     int durationInMinutes;
-    LinkedList<FlightInstance> flightInstances;
+    HashSet<FlightInstance> flightInstances = new HashSet<>();
 
     public Flight(String flightNumber, Airport departure, Airport arrival, int durationInMinutes) {
         this.flightNumber = flightNumber;
@@ -16,7 +17,7 @@ public class Flight {
         this.durationInMinutes = durationInMinutes;
     }
 
-    public LinkedList<FlightInstance> getInstances() {
+    public HashSet<FlightInstance> getInstances() {
         return this.flightInstances;
     }
 

src/test/java/hs/fulda/de/ci/exam/project/FlightTest.java

@@ -2,12 +2,29 @@ package hs.fulda.de.ci.exam.project;
 
 import org.junit.jupiter.api.Test;
 
-import static org.junit.jupiter.api.Assertions.*;
+import java.util.HashSet;
+
+import static org.assertj.core.api.Assertions.*;
 
 class FlightTest {
 
+
+    Address address_fr = new Address("Frankfurt str", "Frankfurt", "Hessen", "63023", "Germany");
+    Airport airport_fr = new Airport("Fraport", address_fr, "1234");
+
+
+    Address address1_ist = new Address("Istanbul str", "Istanbul", "Fatih", "9019", "Turkey");
+    Airport airport1_ist = new Airport("Istanbul", address1_ist, "5678");
+
+    Flight flight1 = new Flight("1", airport_fr, airport1_ist, 140);
+    Flight flight2 = new Flight("2", airport1_ist, airport_fr, 120);
+
+    FlightInstance fInstance1 = new FlightInstance();
+
     @Test
-    void getInstances() {
+    void getInstances_no_instance_should_be_equal() {
+        HashSet<FlightInstance> empty_list = new HashSet<>();
+        assertThat(flight1.getInstances()).describedAs("get flight instances of the flight ").isEqualTo(empty_list);
     }
 
     @Test