tsk-13: Retrieve scheduled message endpoint (#36)

Closes #13

Reviewed-on: phoenix/textsender-api#36
Co-authored-by: phoenix <kundeng00@pm.me>
Co-committed-by: phoenix <kundeng00@pm.me>

internal/store/mock/scheduled_message_store.go

@@ -47,6 +47,32 @@ func (m *MockScheduledMessageStore) Get(ctx context.Context, id uuid.UUID) (*sch
 	}
 }
 
+func (m *MockScheduledMessageStore) GetWithUserId(ctx context.Context, userId uuid.UUID) ([]*scheduling.ScheduledMessage, error) {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+
+	if m.Error != nil {
+		return nil, m.Error
+	}
+
+	if userId == uuid.Nil {
+		return nil, fmt.Errorf("User Id is nil")
+	} else {
+		var schMsgs []*scheduling.ScheduledMessage
+		for _, schMsg := range m.ScheduledMessages {
+			if schMsg.UserId == userId {
+				schMsgs = append(schMsgs, schMsg)
+			}
+		}
+
+		if len(schMsgs) == 0 {
+			return nil, nil
+		} else {
+			return schMsgs, nil
+		}
+	}
+}
+
 func (m *MockScheduledMessageStore) CreateScheduledMessage(ctx context.Context, schedMsg *scheduling.ScheduledMessage) error {
 	m.mu.Lock()
 	defer m.mu.Unlock()