Add Dependency Inversion Principle (DIP) example (2.1/3)

* Add the second iteration of the second stage of our code. Now the `HardcodedInMemoryUsersRepository` will also have its `users` map injected through its constructor. Benefits explained in the test code.

Author: JavierCane

src/main/java/tv/codely/solid_principles/dependency_inversion_principle/stage_2_1_dependency_injection_of_constant_parameters/HardcodedInMemoryUsersRepository.java

@@ -0,0 +1,18 @@
+package tv.codely.solid_principles.dependency_inversion_principle.stage_2_1_dependency_injection_of_constant_parameters;
+
+import tv.codely.solid_principles.dependency_inversion_principle.User;
+
+import java.util.Map;
+import java.util.Optional;
+
+final class HardcodedInMemoryUsersRepository {
+ private Map<Integer, User> users;
+
+ public HardcodedInMemoryUsersRepository(Map<Integer, User> users) {
+ this.users = users;
+ }
+
+ public Optional<User> search(Integer id) {
+ return Optional.ofNullable(users.get(id));
+ }
+}

src/main/java/tv/codely/solid_principles/dependency_inversion_principle/stage_2_1_dependency_injection_of_constant_parameters/UserSearcher.java

@@ -0,0 +1,17 @@
+package tv.codely.solid_principles.dependency_inversion_principle.stage_2_1_dependency_injection_of_constant_parameters;
+
+import tv.codely.solid_principles.dependency_inversion_principle.User;
+
+import java.util.Optional;
+
+final class UserSearcher {
+ private HardcodedInMemoryUsersRepository usersRepository;
+
+ public UserSearcher(HardcodedInMemoryUsersRepository usersRepository) {
+ this.usersRepository = usersRepository;
+ }
+
+ public Optional<User> search(Integer id) {
+ return usersRepository.search(id);
+ }
+}

src/test/java/tv/codely/solid_principles/dependency_inversion_principle/stage_1_instantiating_from_clients/UserSearcherShould.java

@@ -10,21 +10,21 @@
 final class UserSearcherShould {
  @Test
  void find_existing_users() {
+ UserSearcher userSearcher = new UserSearcher();
+
  // We would be coupled to the actual HardcodedInMemoryUsersRepository implementation.
  // We don't have the option to set test users as we would have to do if we had a real database repository.
  Integer existingUserId = 1;
- UserSearcher userSearcher = new UserSearcher();
-
  Optional<User> expectedUser = Optional.of(new User(1, "Rafa"));
 
  assertEquals(expectedUser, userSearcher.search(existingUserId));
  }
 
  @Test
  void not_find_non_existing_users() {
- Integer nonExistingUserId = 5;
  UserSearcher userSearcher = new UserSearcher();
 
+ Integer nonExistingUserId = 5;
  Optional<User> expectedEmptyResult = Optional.empty();
 
  assertEquals(expectedEmptyResult, userSearcher.search(nonExistingUserId));

src/test/java/tv/codely/solid_principles/dependency_inversion_principle/stage_2_1_dependency_injection_of_constant_parameters/UserSearcherShould.java

@@ -0,0 +1,49 @@
+package tv.codely.solid_principles.dependency_inversion_principle.stage_2_1_dependency_injection_of_constant_parameters;
+
+import org.junit.jupiter.api.Test;
+import tv.codely.solid_principles.dependency_inversion_principle.User;
+
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Optional;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+final class UserSearcherShould {
+ @Test
+ void find_existing_users() {
+ // Now we're also injecting the constant parameters needed by the HardcodedInMemoryUsersRepository through its constructor.
+ // 👍 Win: We can send different parameters depending on the environment.
+ // That is, in our production environment we would have actual users,
+ // while in our tests cases we will set only the needed ones to run our test cases
+ int rafaId = 1;
+ User rafa = new User(rafaId, "Rafa");
+
+ Map<Integer, User> users = Collections.unmodifiableMap(new HashMap<Integer, User>() {
+ {
+ put(rafaId, rafa);
+ }
+ });
+ HardcodedInMemoryUsersRepository usersRepository = new HardcodedInMemoryUsersRepository(users);
+ UserSearcher userSearcher = new UserSearcher(usersRepository);
+
+ Optional<User> expectedUser = Optional.of(rafa);
+
+ assertEquals(expectedUser, userSearcher.search(rafaId));
+ }
+
+ @Test
+ void not_find_non_existing_users() {
+ Map<Integer, User> users = Collections.emptyMap();
+ HardcodedInMemoryUsersRepository usersRepository = new HardcodedInMemoryUsersRepository(users);
+ UserSearcher userSearcher = new UserSearcher(usersRepository);
+
+ // 👍 Win: Now we don't have to be coupled of the actual HardcodedInMemoryUsersRepository users.
+ // We can send a random user ID in order to force an empty result because we've set an empty map as the system users.
+ Integer nonExistingUserId = 1;
+ Optional<User> expectedEmptyResult = Optional.empty();
+
+ assertEquals(expectedEmptyResult, userSearcher.search(nonExistingUserId));
+ }
+}