diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
index 91c4481..429ace6 100644
--- a/.pre-commit-config.yaml
+++ b/.pre-commit-config.yaml
@@ -19,7 +19,7 @@ repos:
           - --ignore-init-module-imports
 
   - repo: https://github.com/pycqa/isort
-    rev: 5.10.1
+    rev: 5.11.2
     hooks:
       - id: isort
         name: isort (python)
diff --git a/pyproject.toml b/pyproject.toml
index d8f895f..eafb0cd 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -40,6 +40,11 @@ build-backend = "poetry.core.masonry.api"
 
 [tool.poe.tasks]
 test = { shell = "DATABASE_URL=postgresql://postgres:password@localhost:5433/postgres pytest src" }
+test_domain = "pytest -k domain"
+test_infrastructure = "pytest -k infrastructure"
+test_application = "pytest -k application"
+test_unit = "pytest -m unit"
+test_integration = "pytest -m 'not unit'"
 test_coverage = "pytest --cov=src --cov-report=html"
 start = "uvicorn src.api.main:app --reload"
 start_cli = { shell = "cd src && python -m cli" }
diff --git a/pytest.ini b/pytest.ini
index 85fe117..b4745ab 100644
--- a/pytest.ini
+++ b/pytest.ini
@@ -1,2 +1,7 @@
 [pytest]
-norecursedirs = tmp
\ No newline at end of file
+norecursedirs = tmp
+
+markers =
+    unit: marks test as unit test i.e. not using any external services (deselect with '-m "not unit"') 
+    integration: marks tests as integration i.e. using a database (deselect with '-m "not integration"')
+    serial
\ No newline at end of file
diff --git a/src/api/routers/catalog.py b/src/api/routers/catalog.py
index 892cc00..8752bce 100644
--- a/src/api/routers/catalog.py
+++ b/src/api/routers/catalog.py
@@ -26,7 +26,7 @@ async def get_all_listings(
     query = GetAllListings()
     with module.unit_of_work():
         query_result = module.execute_query(query)
-        return dict(data=query_result.result)
+        return dict(data=query_result.payload)
 
 
 @router.get("/catalog/{listing_id}", tags=["catalog"], response_model=ListingReadModel)
@@ -41,7 +41,7 @@ async def get_listing_details(
     query = GetListingDetails(listing_id=listing_id)
     with module.unit_of_work():
         query_result = module.execute_query(query)
-        return query_result.result
+        return query_result.payload
 
 
 @router.post(
@@ -66,7 +66,7 @@ async def create_listing(
 
         query = GetListingDetails(listing_id=command_result.result)
         query_result = module.execute_query(query)
-        return query_result.result
+        return query_result.payload
 
 
 #
diff --git a/src/api/tests/test_catalog.py b/src/api/tests/test_catalog.py
index b797c84..0f76e65 100644
--- a/src/api/tests/test_catalog.py
+++ b/src/api/tests/test_catalog.py
@@ -1,13 +1,17 @@
+import pytest
+
 from modules.catalog.application.command import CreateListingDraftCommand
 from seedwork.domain.value_objects import Money
 
 
+@pytest.mark.integration
 def test_empty_catalog_list(api_client):
     response = api_client.get("/catalog")
     assert response.status_code == 200
     assert response.json() == {"data": []}
 
 
+@pytest.mark.integration
 def test_catalog_list_with_one_item(api, api_client):
     # arrange
     catalog_module = api.container.catalog_module()
@@ -28,7 +32,7 @@ def test_catalog_list_with_one_item(api, api_client):
     assert response.json() == {
         "data": [
             {
-                "id": str(command_result.result),
+                "id": str(command_result.entity_id),
                 "title": "Foo",
                 "description": "Bar",
                 "ask_price_amount": 10.0,
@@ -38,6 +42,7 @@ def test_catalog_list_with_one_item(api, api_client):
     }
 
 
+@pytest.mark.integration
 def test_catalog_list_with_two_items(api, api_client):
     # arrange
     catalog_module = api.container.catalog_module()
diff --git a/src/api/tests/test_common.py b/src/api/tests/test_common.py
index fc84a1d..580da59 100644
--- a/src/api/tests/test_common.py
+++ b/src/api/tests/test_common.py
@@ -1,3 +1,4 @@
+import pytest
 from fastapi.testclient import TestClient
 
 from api.main import app
@@ -5,11 +6,13 @@
 client = TestClient(app)
 
 
+@pytest.mark.integration
 def test_homepage_returns_200():
     response = client.get("/")
     assert response.status_code == 200
 
 
+@pytest.mark.integration
 def test_docs_page_returns_200():
     response = client.get("/docs")
     assert response.status_code == 200
diff --git a/src/modules/bidding/__init__.py b/src/modules/bidding/__init__.py
index c7891c5..57bb52d 100644
--- a/src/modules/bidding/__init__.py
+++ b/src/modules/bidding/__init__.py
@@ -5,14 +5,6 @@
 )
 from seedwork.application.modules import BusinessModule
 
-#
-# @dataclass
-# class UnitOfWork:
-#     module: Any  # FIXME: type
-#     db_session: Session
-#     correlation_id: uuid.UUID
-#     listing_repository: ListingRepository
-
 
 class BiddingModule(BusinessModule):
     supported_commands = (PlaceBidCommand, RetractBidCommand)
diff --git a/src/modules/bidding/application/command/place_bid.py b/src/modules/bidding/application/command/place_bid.py
index 4fbc077..350ede5 100644
--- a/src/modules/bidding/application/command/place_bid.py
+++ b/src/modules/bidding/application/command/place_bid.py
@@ -23,6 +23,6 @@ def place_bid(
     bid = Bid(bidder=bidder, price=Money(command.amount))
 
     listing: Listing = listing_repository.get_by_id(id=command.listing_id)
-    events = listing.place_bid(bid)
+    listing.place_bid(bid)
 
-    return CommandResult.ok(events=events)
+    return CommandResult.ok()
diff --git a/src/modules/bidding/tests/test_module.py b/src/modules/bidding/tests/domain/__init__.py
similarity index 100%
rename from src/modules/bidding/tests/test_module.py
rename to src/modules/bidding/tests/domain/__init__.py
diff --git a/src/modules/bidding/domain/test_listing.py b/src/modules/bidding/tests/domain/test_listing.py
similarity index 96%
rename from src/modules/bidding/domain/test_listing.py
rename to src/modules/bidding/tests/domain/test_listing.py
index 90d087f..79d504e 100644
--- a/src/modules/bidding/domain/test_listing.py
+++ b/src/modules/bidding/tests/domain/test_listing.py
@@ -8,6 +8,7 @@
 from seedwork.domain.value_objects import UUID
 
 
+@pytest.mark.unit
 def test_listing_initial_price():
     seller = Seller(id=UUID.v4())
     listing = Listing(
@@ -19,6 +20,7 @@ def test_listing_initial_price():
     assert listing.winning_bid is None
 
 
+@pytest.mark.unit
 def test_place_one_bid():
     now = datetime.utcnow()
     seller = Seller(id=UUID.v4())
@@ -34,6 +36,7 @@ def test_place_one_bid():
     assert listing.winning_bid == Bid(Money(20), bidder=bidder, placed_at=now)
 
 
+@pytest.mark.unit
 def test_place_two_bids():
     now = datetime.utcnow()
     seller = Seller(id=UUID.v4())
@@ -50,6 +53,7 @@ def test_place_two_bids():
     assert listing.winning_bid == Bid(Money(30), bidder=bidder2, placed_at=now)
 
 
+@pytest.mark.unit
 def test_place_two_bids_by_same_bidder():
     now = datetime.utcnow()
     seller = Seller(id=UUID.v4())
@@ -67,6 +71,7 @@ def test_place_two_bids_by_same_bidder():
     assert listing.winning_bid == Bid(price=Money(30), bidder=bidder, placed_at=now)
 
 
+@pytest.mark.unit
 def test_cannot_place_bid_if_listing_ended():
     seller = Seller(id=UUID.v4())
     bidder = Bidder(id=UUID.v4())
@@ -88,6 +93,7 @@ def test_cannot_place_bid_if_listing_ended():
         listing.place_bid(bid)
 
 
+@pytest.mark.unit
 def test_retract_bid():
     seller = Seller(id=UUID.v4())
     bidder = Bidder(id=UUID.v4())
@@ -107,6 +113,7 @@ def test_retract_bid():
         listing.retract_bid_of(bidder=bidder)
 
 
+@pytest.mark.unit
 def test_cancel_listing():
     now = datetime.utcnow()
     seller = Seller(id=UUID.v4())
@@ -122,6 +129,7 @@ def test_cancel_listing():
     assert listing.time_left_in_listing == timedelta()
 
 
+@pytest.mark.unit
 def test_can_cancel_listing_with_bids():
     now = datetime.utcnow()
     seller = Seller(id=UUID.v4())
@@ -144,6 +152,7 @@ def test_can_cancel_listing_with_bids():
     assert listing.time_left_in_listing == timedelta()
 
 
+@pytest.mark.unit
 def test_cannot_cancel_listing_with_bids():
     now = datetime.utcnow()
     seller = Seller(id=UUID.v4())
diff --git a/src/modules/bidding/tests/infrastructure/test_listing_repository.py b/src/modules/bidding/tests/infrastructure/test_listing_repository.py
index d14430d..62866ec 100644
--- a/src/modules/bidding/tests/infrastructure/test_listing_repository.py
+++ b/src/modules/bidding/tests/infrastructure/test_listing_repository.py
@@ -1,6 +1,8 @@
 import datetime
 import uuid
 
+import pytest
+
 from modules.bidding.domain.entities import Bid, Bidder, Listing, Money, Seller
 from modules.bidding.infrastructure.listing_repository import (
     ListingDataMapper,
@@ -10,11 +12,13 @@
 from seedwork.domain.value_objects import UUID
 
 
+@pytest.mark.integration
 def test_listing_repo_is_empty(db_session):
     repo = PostgresJsonListingRepository(db_session=db_session)
     assert repo.count() == 0
 
 
+@pytest.mark.unit
 def test_listing_data_mapper_maps_entity_to_model():
     listing = Listing(
         id=UUID("00000000000000000000000000000001"),
@@ -58,6 +62,7 @@ def test_listing_data_mapper_maps_entity_to_model():
     assert actual.data == expected.data
 
 
+@pytest.mark.unit
 def test_listing_data_mapper_maps_model_to_entity():
     instance = ListingModel(
         id=UUID("00000000000000000000000000000001"),
@@ -83,6 +88,7 @@ def test_listing_data_mapper_maps_model_to_entity():
     assert actual == expected
 
 
+@pytest.mark.integration
 def test_listing_persistence(db_session):
     original = Listing(
         id=Listing.next_id(),
diff --git a/src/modules/catalog/application/command/create_listing_draft.py b/src/modules/catalog/application/command/create_listing_draft.py
index 0de4b4c..0ea9a14 100644
--- a/src/modules/catalog/application/command/create_listing_draft.py
+++ b/src/modules/catalog/application/command/create_listing_draft.py
@@ -31,6 +31,6 @@ def create_listing_draft(
         seller_id=command.seller_id,
     )
     repository.add(listing)
-    return CommandResult.ok(
-        result=listing.id, events=[ListingDraftCreatedEvent(listing_id=listing.id)]
+    return CommandResult.success(
+        entity_id=listing.id, events=[ListingDraftCreatedEvent(listing_id=listing.id)]
     )
diff --git a/src/modules/catalog/application/command/publish_listing.py b/src/modules/catalog/application/command/publish_listing.py
index 7b6e425..b12ddc4 100644
--- a/src/modules/catalog/application/command/publish_listing.py
+++ b/src/modules/catalog/application/command/publish_listing.py
@@ -27,4 +27,4 @@ def publish_listing(
 
     events = seller.publish_listing(listing)
 
-    return CommandResult.ok(events=events)
+    return CommandResult.success(entity_id=listing.id, events=events)
diff --git a/src/modules/catalog/application/command/update_listing_draft.py b/src/modules/catalog/application/command/update_listing_draft.py
index cd2071d..c16de09 100644
--- a/src/modules/catalog/application/command/update_listing_draft.py
+++ b/src/modules/catalog/application/command/update_listing_draft.py
@@ -29,4 +29,4 @@ def update_listing_draft(
         description=command.description,
         ask_price=command.ask_price,
     )
-    return CommandResult.ok(events=events)
+    return CommandResult.success(entity_id=listing.id, events=events)
diff --git a/src/modules/catalog/application/query/get_all_listings.py b/src/modules/catalog/application/query/get_all_listings.py
index 13dcf86..652e2b7 100644
--- a/src/modules/catalog/application/query/get_all_listings.py
+++ b/src/modules/catalog/application/query/get_all_listings.py
@@ -19,6 +19,6 @@ def get_all_listings(
     session: Session,
 ) -> QueryResult:
     queryset = session.query(ListingModel)
-    result = [map_listing_model_to_dao(row) for row in queryset.all()]
+    payload = [map_listing_model_to_dao(row) for row in queryset.all()]
     # TODO: add error handling
-    return QueryResult.ok(result)
+    return QueryResult.success(payload)
diff --git a/src/modules/catalog/tests/application/test_create_listing_draft.py b/src/modules/catalog/tests/application/test_create_listing_draft.py
new file mode 100644
index 0000000..1c46285
--- /dev/null
+++ b/src/modules/catalog/tests/application/test_create_listing_draft.py
@@ -0,0 +1,25 @@
+import pytest
+
+from modules.catalog.application.command.create_listing_draft import (
+    CreateListingDraftCommand,
+    create_listing_draft,
+)
+from modules.catalog.domain.entities import Seller
+from seedwork.domain.value_objects import Money
+from seedwork.infrastructure.repository import InMemoryRepository
+
+
+@pytest.mark.unit
+def test_create_listing_draft():
+    # arrange
+    command = CreateListingDraftCommand(
+        title="foo", description="bar", ask_price=Money(1), seller_id=Seller.next_id()
+    )
+    repository = InMemoryRepository()
+
+    # act
+    result = create_listing_draft(command, repository)
+
+    # assert
+    assert repository.get_by_id(result.entity_id).title == "foo"
+    assert result.has_errors() is False
diff --git a/src/modules/catalog/tests/application/test_command_handlers.py b/src/modules/catalog/tests/application/test_publish_listing.py
similarity index 57%
rename from src/modules/catalog/tests/application/test_command_handlers.py
rename to src/modules/catalog/tests/application/test_publish_listing.py
index a1e9b94..7540c1d 100644
--- a/src/modules/catalog/tests/application/test_command_handlers.py
+++ b/src/modules/catalog/tests/application/test_publish_listing.py
@@ -1,63 +1,16 @@
-from modules.catalog.application.command.create_listing_draft import (
-    CreateListingDraftCommand,
-    create_listing_draft,
-)
+import pytest
+
 from modules.catalog.application.command.publish_listing import (
     PublishListingCommand,
     publish_listing,
 )
-from modules.catalog.application.command.update_listing_draft import (
-    UpdateListingDraftCommand,
-    update_listing_draft,
-)
 from modules.catalog.domain.entities import Listing, Seller
 from modules.catalog.domain.value_objects import ListingStatus
-from seedwork.domain.value_objects import UUID, Money
+from seedwork.domain.value_objects import Money
 from seedwork.infrastructure.repository import InMemoryRepository
 
 
-def test_create_listing_draft():
-    # arrange
-    command = CreateListingDraftCommand(
-        title="foo", description="bar", ask_price=Money(1), seller_id=Seller.next_id()
-    )
-    repository = InMemoryRepository()
-
-    # act
-    result = create_listing_draft(command, repository)
-
-    # assert
-    assert repository.get_by_id(result.result).title == "foo"
-    assert result.has_errors() is False
-
-
-def test_update_listing_draft():
-    # arrange
-    repository = InMemoryRepository()
-    listing = Listing(
-        id=Listing.next_id(),
-        title="Tiny dragon",
-        description="Tiny dragon for sale",
-        ask_price=Money(1),
-        seller_id=UUID.v4(),
-    )
-    repository.add(listing)
-
-    command = UpdateListingDraftCommand(
-        listing_id=listing.id,
-        title="Tiny golden dragon",
-        description=listing.description,
-        ask_price=listing.ask_price,
-        modify_user_id=listing.seller_id,
-    )
-
-    # act
-    result = update_listing_draft(command, repository)
-
-    # assert
-    assert result.is_ok()
-
-
+@pytest.mark.unit
 def test_publish_listing():
     # arrange
     seller_repository = InMemoryRepository()
@@ -87,10 +40,11 @@ def test_publish_listing():
     )
 
     # assert
-    assert result.is_ok()
+    assert result.is_success()
     assert listing.status == ListingStatus.PUBLISHED
 
 
+@pytest.mark.unit
 def test_publish_listing_and_break_business_rule():
     # arrange
     seller_repository = InMemoryRepository()
diff --git a/src/modules/catalog/tests/application/test_update_listing_draft.py b/src/modules/catalog/tests/application/test_update_listing_draft.py
new file mode 100644
index 0000000..2f24d06
--- /dev/null
+++ b/src/modules/catalog/tests/application/test_update_listing_draft.py
@@ -0,0 +1,37 @@
+import pytest
+
+from modules.catalog.application.command.update_listing_draft import (
+    UpdateListingDraftCommand,
+    update_listing_draft,
+)
+from modules.catalog.domain.entities import Listing
+from seedwork.domain.value_objects import UUID, Money
+from seedwork.infrastructure.repository import InMemoryRepository
+
+
+@pytest.mark.unit
+def test_update_listing_draft():
+    # arrange
+    repository = InMemoryRepository()
+    listing = Listing(
+        id=Listing.next_id(),
+        title="Tiny dragon",
+        description="Tiny dragon for sale",
+        ask_price=Money(1),
+        seller_id=UUID.v4(),
+    )
+    repository.add(listing)
+
+    command = UpdateListingDraftCommand(
+        listing_id=listing.id,
+        title="Tiny golden dragon",
+        description=listing.description,
+        ask_price=listing.ask_price,
+        modify_user_id=listing.seller_id,
+    )
+
+    # act
+    result = update_listing_draft(command, repository)
+
+    # assert
+    assert result.is_success()
diff --git a/src/modules/catalog/tests/domain/test_entities.py b/src/modules/catalog/tests/domain/test_entities.py
index 93b653f..9ff52c8 100644
--- a/src/modules/catalog/tests/domain/test_entities.py
+++ b/src/modules/catalog/tests/domain/test_entities.py
@@ -6,6 +6,7 @@
 from seedwork.domain.value_objects import Money
 
 
+@pytest.mark.unit
 def test_seller_publishes_listing_happy_path():
     seller = Seller(id=Seller.next_id())
     listing = Listing(
@@ -21,6 +22,7 @@ def test_seller_publishes_listing_happy_path():
     assert listing.status == ListingStatus.PUBLISHED
 
 
+@pytest.mark.unit
 def test_seller_fails_to_publish_listing_with_zero_price():
     seller = Seller(id=Seller.next_id())
     listing = Listing(
diff --git a/src/modules/catalog/tests/domain/test_rules.py b/src/modules/catalog/tests/domain/test_rules.py
index dfcdcaf..9ad5e8f 100644
--- a/src/modules/catalog/tests/domain/test_rules.py
+++ b/src/modules/catalog/tests/domain/test_rules.py
@@ -1,12 +1,16 @@
+import pytest
+
 from modules.catalog.domain.rules import ListingAskPriceMustBeGreaterThanZero
 from seedwork.domain.value_objects import Money
 
 
+@pytest.mark.unit
 def test_AuctionItemPriceMustBeGreaterThanZero_rule():
     rule = ListingAskPriceMustBeGreaterThanZero(ask_price=Money(1))
     assert not rule.is_broken()
 
 
+@pytest.mark.unit
 def test_AuctionItemPriceMustBeGreaterThanZero_rule_is_broken():
     rule = ListingAskPriceMustBeGreaterThanZero(ask_price=Money(0))
     assert rule.is_broken()
diff --git a/src/modules/catalog/tests/infrastructure/test_listing_repository.py b/src/modules/catalog/tests/infrastructure/test_listing_repository.py
index 291d976..21f1062 100644
--- a/src/modules/catalog/tests/infrastructure/test_listing_repository.py
+++ b/src/modules/catalog/tests/infrastructure/test_listing_repository.py
@@ -1,3 +1,5 @@
+import pytest
+
 from modules.catalog.domain.entities import Listing, Money
 from modules.catalog.infrastructure.listing_repository import (
     ListingDataMapper,
@@ -9,11 +11,13 @@
 # engine = sqlalchemy.create_engine("")
 
 
+@pytest.mark.integration
 def test_listing_repo_is_empty(db_session):
     repo = PostgresJsonListingRepository(db_session=db_session)
     assert repo.count() == 0
 
 
+@pytest.mark.unit
 def test_listing_data_mapper_maps_entity_to_model():
     listing = Listing(
         id=UUID("00000000000000000000000000000001"),
@@ -43,6 +47,7 @@ def test_listing_data_mapper_maps_entity_to_model():
     assert actual.data == expected.data
 
 
+@pytest.mark.unit
 def test_listing_data_mapper_maps_model_to_entity():
     instance = ListingModel(
         id=UUID("00000000000000000000000000000001"),
@@ -71,6 +76,7 @@ def test_listing_data_mapper_maps_model_to_entity():
     assert actual == expected
 
 
+@pytest.mark.integration
 def test_listing_persistence(db_session):
     original = Listing(
         id=Listing.next_id(),
diff --git a/src/seedwork/application/command_handlers.py b/src/seedwork/application/command_handlers.py
index c1915ea..7591e2e 100644
--- a/src/seedwork/application/command_handlers.py
+++ b/src/seedwork/application/command_handlers.py
@@ -1,74 +1,39 @@
 import sys
+from dataclasses import dataclass, field
 from typing import Any
 
-from pydantic import BaseModel
-
 from seedwork.domain.type_hints import DomainEvent
+from seedwork.domain.value_objects import UUID
 
 
-class CommandResult(BaseModel):
-    result: Any = None
-    events: list[DomainEvent] = []
-    errors: list[Any] = []
-
-    # # commands
-    # def add_error(self, message, exception=None, exception_info=None):
-    #     self.__errors.append((message, exception, exception_info))
-    #     return self
-
-    # # queries
-    # @property
-    # def result(self) -> Any:
-    #     """Shortcut to get_result()"""
-    #     return self.get_result()
-    #
-    # def get_result(self) -> Any:
-    #     """Gets result"""
-    #     assert (
-    #         not self.has_errors()
-    #     ), f"Cannot access result. QueryResult has errors.\n  Errors: {self.__errors}"
-    #     return self.__result
-    #
-    # @property
-    # def events(self) -> List[DomainEvent]:
-    #     """Shortcut to get_events()"""
-    #     return self.get_events()
-    #
-    # def get_events(self) -> List[DomainEvent]:
-    #     """Gets result"""
-    #     assert (
-    #         not self.has_errors()
-    #     ), f"Cannot access events. QueryResult has errors.\n  Errors: {self.__errors}"
-    #     return self.__events
-    #
-    # def get_errors(self):
-    #     return self.__errors
+@dataclass
+class CommandResult:
+    entity_id: UUID = None
+    payload: Any = None
+    events: list[DomainEvent] = field(default_factory=list)
+    errors: list[Any] = field(default_factory=list)
 
     def has_errors(self):
         return len(self.errors) > 0
 
-    def is_ok(self) -> bool:
+    def is_success(self) -> bool:
         return not self.has_errors()
 
     @classmethod
-    def ok(cls, result=None, events=[]) -> "CommandResult":
-        """Creates a successful result"""
-        return cls(result=result, events=events)
-
-    @classmethod
-    def failed(cls, message="Failure", exception=None) -> "CommandResult":
+    def failure(cls, message="Failure", exception=None) -> "CommandResult":
         """Creates a failed result"""
         exception_info = sys.exc_info()
         errors = [(message, exception, exception_info)]
         result = cls(errors=errors)
         return result
 
-
-class QueryHandler:
-    """
-    Base query handler class
-    """
+    @classmethod
+    def success(cls, entity_id=None, payload=None, events=[]) -> "CommandResult":
+        """Creates a successful result"""
+        return cls(entity_id=entity_id, payload=payload, events=events)
 
 
 class CommandHandler:
-    pass
+    """
+    Base class for command handlers
+    """
diff --git a/src/seedwork/application/decorators.py b/src/seedwork/application/decorators.py
index 17afd80..c36cd6e 100644
--- a/src/seedwork/application/decorators.py
+++ b/src/seedwork/application/decorators.py
@@ -75,9 +75,9 @@ def decorator(*args, **kwargs):
             )
             return fn(*args, **kwargs)
         except ValidationError as e:
-            return CommandResult.failed("Validation error", exception=e)
+            return CommandResult.failure("Validation error", exception=e)
         except BusinessRuleValidationException as e:
-            return CommandResult.failed("Business rule validation error", exception=e)
+            return CommandResult.failure("Business rule validation error", exception=e)
 
     handler_signature = signature(fn)
     kwargs_iterator = iter(handler_signature.parameters.items())
diff --git a/src/seedwork/application/query_handlers.py b/src/seedwork/application/query_handlers.py
index 2376c04..b27cd49 100644
--- a/src/seedwork/application/query_handlers.py
+++ b/src/seedwork/application/query_handlers.py
@@ -1,46 +1,34 @@
+import sys
+from dataclasses import dataclass, field
+from typing import Any
+
+
+@dataclass
 class QueryResult:
-    def __init__(self, result) -> None:
-        self.__result = result
-        self.__errors = []
-
-    # commands
-    def add_error(self, message, exception=None):
-        self.__errors.append((message, exception))
-        return self
-
-    # queries
-    @property
-    def result(self):
-        """Shortcut to get_result()"""
-        return self.get_result()
-
-    def get_result(self):
-        """Gets result"""
-        assert (
-            not self.has_errors()
-        ), f"Cannot access result. QueryResult has errors.\n  Errors: {self.__errors}"
-        return self.__result
+    payload: Any = None
+    errors: list[Any] = field(default_factory=list)
 
     def has_errors(self):
-        return len(self.__errors) > 0
+        return len(self.errors) > 0
 
-    def is_ok(self):
+    def is_success(self) -> bool:
         return not self.has_errors()
 
     @classmethod
-    def ok(cls, result):
-        """Creates a successful result"""
-        return cls(result=result)
-
-    @classmethod
-    def failed(cls, message="Failure", exception=None):
+    def failure(cls, message="Failure", exception=None) -> "QueryResult":
         """Creates a failed result"""
-        result = cls()
-        result.add_error(message, exception)
+        exception_info = sys.exc_info()
+        errors = [(message, exception, exception_info)]
+        result = cls(errors=errors)
         return result
 
+    @classmethod
+    def success(cls, payload=None) -> "QueryResult":
+        """Creates a successful result"""
+        return cls(payload=payload)
+
 
 class QueryHandler:
     """
-    Base query handler class
+    Base class for query handlers
     """
diff --git a/src/seedwork/tests/application/test_decorators.py b/src/seedwork/tests/application/test_decorators.py
index 65d0f09..d6dfe3f 100644
--- a/src/seedwork/tests/application/test_decorators.py
+++ b/src/seedwork/tests/application/test_decorators.py
@@ -1,10 +1,13 @@
 from dataclasses import dataclass
 
+import pytest
+
 from seedwork.application.commands import Command
 from seedwork.application.decorators import command_handler, query_handler, registry
 from seedwork.application.queries import Query
 
 
+@pytest.mark.unit
 def test_command_handler_decorator_registers_command_handler():
     registry.clear()
 
@@ -20,6 +23,7 @@ def foo_command_handler(command: FooCommand):
     assert registry.get_command_handler_parameters_for(FooCommand) == {}
 
 
+@pytest.mark.unit
 def test_command_handler_decorator_does_not_register_command_handler_if_type_mismatch():
     registry.clear()
 
@@ -38,6 +42,7 @@ def foo_command_handler(command: BarCommand):
     assert FooCommand not in registry.command_handlers
 
 
+@pytest.mark.unit
 def test_query_handler_decorator_registers_query_handler():
     registry.clear()
 
diff --git a/src/seedwork/tests/application/test_module.py b/src/seedwork/tests/application/test_module.py
index e69de29..022fc16 100644
--- a/src/seedwork/tests/application/test_module.py
+++ b/src/seedwork/tests/application/test_module.py
@@ -0,0 +1 @@
+# TODO: add business module tests
diff --git a/src/seedwork/tests/domain/test_entity.py b/src/seedwork/tests/domain/test_entity.py
index b1c498f..17daecb 100644
--- a/src/seedwork/tests/domain/test_entity.py
+++ b/src/seedwork/tests/domain/test_entity.py
@@ -1,5 +1,7 @@
 from dataclasses import dataclass
 
+import pytest
+
 from seedwork.domain.entities import AggregateRoot, Entity
 
 
@@ -13,11 +15,13 @@ class PersonAggregate(AggregateRoot):
     name: str
 
 
+@pytest.mark.unit
 def test_entity():
     bob = PersonEntity(id=PersonEntity.next_id(), name="Bob")
     assert bob.id is not None
 
 
+@pytest.mark.unit
 def test_aggregate():
     bob = PersonAggregate(id=PersonEntity.next_id(), name="Bob")
     assert bob.id is not None
diff --git a/src/seedwork/domain/test_value_objects.py b/src/seedwork/tests/domain/test_value_objects.py
similarity index 79%
rename from src/seedwork/domain/test_value_objects.py
rename to src/seedwork/tests/domain/test_value_objects.py
index be9e0a3..7ffb5ec 100644
--- a/src/seedwork/domain/test_value_objects.py
+++ b/src/seedwork/tests/domain/test_value_objects.py
@@ -1,9 +1,13 @@
+import pytest
+
 from seedwork.domain.value_objects import Money
 
 
+@pytest.mark.unit
 def test_money_equality():
     assert Money(10, "USD") == Money(10, "USD")
 
 
+@pytest.mark.unit
 def test_money_ordering():
     assert Money(10, "USD") < Money(100, "USD")
diff --git a/src/seedwork/tests/infrastructure/test_data_mapper.py b/src/seedwork/tests/infrastructure/test_data_mapper.py
index b4583be..1f0beb7 100644
--- a/src/seedwork/tests/infrastructure/test_data_mapper.py
+++ b/src/seedwork/tests/infrastructure/test_data_mapper.py
@@ -1,6 +1,8 @@
 from dataclasses import dataclass
 from uuid import UUID
 
+import pytest
+
 from seedwork.domain.entities import Entity
 from seedwork.infrastructure.data_mapper import JSONDataMapper
 
@@ -17,6 +19,7 @@ class PersonJSONDataMapper(JSONDataMapper):
     model_class = dict
 
 
+@pytest.mark.unit
 def test_data_mapper_maps_entity_to_json():
     mapper = PersonJSONDataMapper()
     entity_instance = PersonEntity(
@@ -30,6 +33,7 @@ def test_data_mapper_maps_entity_to_json():
     assert actual == expected
 
 
+@pytest.mark.unit
 def test_data_mapper_maps_json_to_entity():
     mapper = PersonJSONDataMapper()
     model_instance = {
diff --git a/src/seedwork/infrastructure/test_repository.py b/src/seedwork/tests/infrastructure/test_repository.py
similarity index 94%
rename from src/seedwork/infrastructure/test_repository.py
rename to src/seedwork/tests/infrastructure/test_repository.py
index 44e1bdb..0477100 100644
--- a/src/seedwork/infrastructure/test_repository.py
+++ b/src/seedwork/tests/infrastructure/test_repository.py
@@ -1,5 +1,7 @@
 from dataclasses import dataclass
 
+import pytest
+
 from seedwork.domain.entities import Entity
 from seedwork.infrastructure.repository import InMemoryRepository
 
@@ -10,6 +12,7 @@ class Person(Entity):
     last_name: str
 
 
+@pytest.mark.unit
 def test_InMemoryRepository_persist_one():
     # arrange
     person = Person(id=Person.next_id(), first_name="John", last_name="Doe")
@@ -22,6 +25,7 @@ def test_InMemoryRepository_persist_one():
     assert repository.get_by_id(person.id) == person
 
 
+@pytest.mark.unit
 def test_InMemoryRepository_persist_two():
     # arrange
     person1 = Person(id=Person.next_id(), first_name="John", last_name="Doe")