diff --git a/conftest.py b/conftest.py
new file mode 100644
index 0000000..cc8cd0d
--- /dev/null
+++ b/conftest.py
@@ -0,0 +1,85 @@
+import pytest
+from users.models import User, Team, Role
+from tasks.models import Task, Priority, Status
+
+DEFAULT_VALID_PASSWORD = "ssSSAD231!@"
+DEFAULT_MAIL_EXTENSION = "@redhat.com"
+DEFAULT_DATA_DESCRIPTION = "This is test data"
+
+
+@pytest.fixture
+def teams():
+    """
+    Adds teams to DB
+    """
+
+    return tuple(Team.objects.create(name=f"Team{i}",
+                                     description=DEFAULT_DATA_DESCRIPTION)
+                 for i in range(1, 4))
+
+
+@pytest.fixture
+def users(teams):
+    """
+    Adds users to DB
+    """
+    team1, team2, team3 = teams
+    employees = []
+    managers = []
+    users_counter = 0
+    for i in range(3):
+        for team in (team1, team2):
+            employee = User.create_user(username=f"User{users_counter}",
+                                        email=f"User{users_counter}{DEFAULT_MAIL_EXTENSION}",
+                                        password=DEFAULT_VALID_PASSWORD,
+                                        first_name=f"User{users_counter}",
+                                        last_name=f"User{users_counter}",
+                                        role=Role.EMPLOYEE,
+                                        team=team)
+            employees.append(employee)
+            users_counter += 1
+    for i, team in enumerate((team1, team2, team3)):
+        manager = User.create_user(username=f"Manager{i}",
+                                   email=f"Manager{i}{DEFAULT_MAIL_EXTENSION}",
+                                   password=DEFAULT_VALID_PASSWORD,
+                                   first_name=f"Manager{i}",
+                                   last_name=f"Manager{i}",
+                                   role=Role.MANAGER,
+                                   team=team)
+        managers.append(manager)
+    return teams, tuple(employees), tuple(managers)
+
+
+@pytest.fixture
+def tasks(users):
+    """
+    Adds tasks to DB
+    """
+    teams, employees, managers = users
+    tasks = []
+    tasks_counter = 0
+    for team in teams:
+        team_employees = User.objects.filter(team=team, role=Role.EMPLOYEE)
+        team_manager = User.objects.filter(team=team, role=Role.MANAGER).first()
+        for employee in team_employees:
+            task = Task.objects.create(title=f"Task{tasks_counter}",
+                                       assignee=employee,
+                                       created_by=team_manager,
+                                       priority=Priority.LOW,
+                                       status=Status.BACKLOG,
+                                       description=DEFAULT_DATA_DESCRIPTION)
+            tasks.append(task)
+        return teams, employees, managers, tuple(tasks)
+
+
+@pytest.fixture
+def test_db(tasks):
+    """
+    Returns test DB components as tuples.
+    The test DB contains: 3 teams, 3 users per team, 2 tasks per user, 1 manager per team.
+    """
+    teams = tasks[0]
+    employees = tasks[1]
+    managers = tasks[2]
+    task = tasks[3]
+    return teams, employees, managers, task
diff --git a/tasks/models.py b/tasks/models.py
index c84a870..15bd2fe 100644
--- a/tasks/models.py
+++ b/tasks/models.py
@@ -53,6 +53,16 @@ def filter_by_symbol(cls, priority_filter):
         print(priority_filter)
         return cls.objects.filter(priority=priority_filter)
 
+    def change_assignee(self, new_assignee):
+        if new_assignee not in User.objects.all():
+            raise Exception
+        prev_assignee = self.assignee
+        if new_assignee is None:
+            raise TypeError("Valid user must be provided")
+        if new_assignee.team != prev_assignee.team:
+            raise ValueError("The new assignee must be of the same team")
+        self.assignee = new_assignee
+
     @classmethod
     @transaction.atomic
     def create_task(cls, title, assignee, created_by, priority, status, description):
diff --git a/tasks/tests/test_change_assignee.py b/tasks/tests/test_change_assignee.py
new file mode 100644
index 0000000..fd11ac4
--- /dev/null
+++ b/tasks/tests/test_change_assignee.py
@@ -0,0 +1,53 @@
+import pytest
+from tasks.models import Task
+from users.models import Team, User, Role
+from django.contrib.auth.models import User as DjangoUser
+
+
+@pytest.mark.django_db
+class TestChangeTaskAssignee:
+    def test_change_task_assignee(self, test_db):
+        team = test_db[0][0]
+        employee_1, employee_2 = User.objects.filter(team=team)[:2]
+        task = Task.objects.filter(assignee=employee_1).first()
+        assert task is not None
+        assert task.assignee == employee_1
+        task.change_assignee(employee_2)
+        assert task.assignee == employee_2
+
+    @pytest.mark.parametrize("invalid_input", ["INVALID VALUE", None, 2])
+    def test_change_assignee_invalid_input(self, test_db, invalid_input):
+        _, _, _, tasks = test_db
+        task = tasks[0]
+        assignee = task.assignee
+        with pytest.raises(Exception):
+            task.change_assignee(invalid_input)
+        assert assignee == task.assignee
+
+    def test_change_assignee_other_team(self, test_db):
+        teams = Team.objects.all()
+        assert len(teams) >= 2
+        team_1 = teams[0]
+        team_2 = teams[1]
+        employee_1 = User.objects.filter(team=team_1).first()
+        employee_2 = User.objects.filter(team=team_2).first()
+        task = Task.objects.filter(assignee=employee_1).first()
+        with pytest.raises(Exception):
+            task.change_assignee(employee_2)
+        assert task.assignee == employee_1
+
+    @pytest.fixture
+    def out_db_user(self, test_db):
+        team = test_db[0][0]
+        django_user = DjangoUser.objects.create(username="testtest",
+                                                password="ssdalhSFDAJ23!",
+                                                email="example@redhat.com",
+                                                first_name="test",
+                                                last_name="test")
+        user = User(user=django_user, role=Role.EMPLOYEE, team=team)
+        return user
+
+    def test_change_assignee_not_db_user(self, test_db, out_db_user):
+        task = test_db[3][0]
+        with pytest.raises(Exception):
+            task.change_assignee(out_db_user)