Update CityListTest.java

app/src/main/java/com/example/simpleparadox/listycity/CityList.java

@@ -9,6 +9,19 @@
  */
 public class CityList {
     private List<City> cities = new ArrayList<>();
+
+    /**
+     * This adds a city to the list if the city does not exist
+     * @param city
+     *      This is a candidate city to add
+     */
+    public void addOne(City city) {
+        if (hasCity(city)) {
+            throw new IllegalArgumentException();
+        }
+        cities.add(city);
+    }
+
 
     /**
      * This adds a city to the list if the city does not exist

app/src/test/java/com/example/simpleparadox/listycity/CityListTest.java

@@ -93,4 +93,11 @@ void testCountCities() {
 
         assertEquals(1, cityList.countCities());
     }
-}
+
+    @Test
+    void testTwoCities(){
+        CityList cityList = mockCityList();
+        cityList.addOne(new City("Regina", "Saskatchewan"));
+        assertEquals(2,cityList.countCities());
+    }
+}