Unit test

app/src/main/java/com/example/citylist/City.java

@@ -1,6 +1,6 @@
 package com.example.citylist;
 
-public class City {
+public class City implements Comparable<City>{
     private String city;
     private String province;
 
@@ -16,4 +16,9 @@ String getCityName(){
     String getProvinceName(){
         return this.province;
     }
-}
+
+    @Override
+    public int compareTo(City city) {
+        return this.city.compareTo(city.getCityName());
+    }
+}

app/src/main/java/com/example/citylist/CityList.java

@@ -0,0 +1,35 @@
+package com.example.citylist;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+
+/**
+ * This is a class that keeps track of a list of city objects
+ */
+public class CityList {
+    private List<City> cities = new ArrayList<>();
+
+    /**
+     * This adds a city to the list if that city does not exist
+     * @param city
+     *      This is the city to add
+     */
+    public void add(City city) {
+        if (cities.contains(city)) {
+            throw new IllegalArgumentException();
+        }
+        cities.add(city);
+    }
+
+    /**
+     * This returns a sorted list of cities
+     * @return
+     *      Return the sorted list of cities
+     */
+    public List<City> getCities() {
+        List<City> cityList = cities;
+        Collections.sort(cityList);
+        return cityList;
+    }
+}

app/src/test/java/com/example/citylist/CityListTest.java

@@ -0,0 +1,52 @@
+package com.example.citylist;
+
+import org.junit.Test;
+
+import static org.junit.Assert.*;
+
+public class CityListTest {
+    private CityList mockCityList() {
+        CityList cityList = new CityList();
+        cityList.add(mockCity());
+        return cityList;
+    }
+
+    private City mockCity() {
+        return new City("Edmonton", "AB");
+    }
+
+    @Test
+    public void testAdd() {
+        CityList cityList = mockCityList();
+        assertEquals(1, cityList.getCities().size());
+
+        City city = new City("Regina", "SK");
+        cityList.add(city);
+
+        assertEquals(2, cityList.getCities().size());
+        assertTrue(cityList.getCities().contains(city));
+    }
+
+    @Test
+    public void testAddException() {
+        CityList cityList = new CityList();
+        City city = mockCity();
+        cityList.add(city);
+
+        assertThrows(IllegalArgumentException.class, () -> {
+            cityList.add(city);
+        });
+    }
+
+    @Test
+    public void testGetCities() {
+        CityList cityList = mockCityList();
+        assertEquals(0, mockCity().compareTo(cityList.getCities().get(0)));
+
+        City city = new City("Charlottetown", "Prince Edward Island");
+        cityList.add(city);
+
+        assertEquals(0, city.compareTo(cityList.getCities().get(0)));
+        assertEquals(0, mockCity().compareTo(cityList.getCities().get(1)));
+    }
+}