add aircraft parameters should not be null or negative

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

@@ -135,4 +135,17 @@ public class AdminTest {
             admin.addAircraft("Boeing", "787", 2003);
         });
     }
+    @Test
+    public void addAircraftShouldThrowRuntimeExceptionWhenNull(){
+
+        assertThrows(RuntimeException.class, () -> {
+            admin.addAircraft(null, "787", 2003);
+        });
+        assertThrows(RuntimeException.class, () -> {
+            admin.addAircraft("Boeing", "", 2003);
+        });
+        assertThrows(RuntimeException.class, () -> {
+            admin.addAircraft("Boeing", "787", -2003);
+        });
+    }
 }