Implemenet storage layer

Implementation for an in-memory database used to store tasks.

src/main/java/taskmanagement/storage/InMemoryTaskManagementRepository.java

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+package taskmanagement.storage;
+
+import taskmanagement.service.Task;
+import taskmanagement.service.TaskManagementRepository;
+
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Optional;
+import java.util.stream.Collectors;
+
+public class InMemoryTaskManagementRepository implements TaskManagementRepository {
+
+    Map<String, Task> tasks = new HashMap<>();
+
+    @Override
+    public void save(Task task) {
+        tasks.put(task.getIdentifier(), task);
+    }
+
+    @Override
+    public List<Task> getAll() {
+        return tasks.values().stream()
+                .collect(Collectors.toUnmodifiableList());
+    }
+
+    @Override
+    public Optional<Task> get(String taskID) {
+        return Optional.ofNullable(tasks.get(taskID));
+    }
+
+    @Override
+    public void delete(String taskID) {
+        tasks.remove(taskID);
+    }
+
+}

src/test/java/taskmanagement/storage/InMemoryTaskManagementRepositoryTest.java

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+package taskmanagement.storage;
+
+
+import org.junit.Test;
+import taskmanagement.service.Task;
+
+import java.util.HashSet;
+import java.util.List;
+import java.util.Optional;
+import java.util.Set;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertSame;
+import static org.junit.Assert.assertTrue;
+
+public class InMemoryTaskManagementRepositoryTest {
+
+    @Test
+    public void testSaveAndGet() {
+        InMemoryTaskManagementRepository repository = new InMemoryTaskManagementRepository();
+
+        Task task = Task.builder("test-title", "test-description").build();
+
+        repository.save(task);
+
+        Optional<Task> retrievedTask = repository.get(task.getIdentifier());
+
+        assertTrue(retrievedTask.isPresent());
+        assertSame(task, retrievedTask.get());
+    }
+
+    @Test
+    public void testSaveAndGetAll() {
+        InMemoryTaskManagementRepository repository = new InMemoryTaskManagementRepository();
+
+        assertTrue(repository.getAll().isEmpty());
+
+        Task task = Task.builder("test-title", "test-description").build();
+        Task anotherTask = Task.builder("another-test-title", "another-test-description").build();
+
+        repository.save(task);
+        repository.save(anotherTask);
+
+        List<Task> retrievedTasks = repository.getAll();
+
+        Set<Task> expectedTasks = new HashSet<>();
+        expectedTasks.add(task);
+        expectedTasks.add(anotherTask);
+
+        assertEquals(new HashSet<>(retrievedTasks), expectedTasks);
+    }
+
+    @Test
+    public void testSaveDeleteAndGet() {
+        InMemoryTaskManagementRepository repository = new InMemoryTaskManagementRepository();
+
+        Task task = Task.builder("test-title", "test-description").build();
+
+        repository.save(task);
+
+        Optional<Task> retrievedTask = repository.get(task.getIdentifier());
+
+        assertTrue(retrievedTask.isPresent());
+        assertSame(task, retrievedTask.get());
+
+        repository.delete(task.getIdentifier());
+
+        retrievedTask = repository.get(task.getIdentifier());
+        assertFalse(retrievedTask.isPresent());
+    }
+}