diff --git a/c8y_api/app/__init__.py b/c8y_api/app/__init__.py
index 29025c7..d3bacc9 100644
--- a/c8y_api/app/__init__.py
+++ b/c8y_api/app/__init__.py
@@ -343,3 +343,6 @@ def _get_tenant_instance(self, tenant_id: str) -> CumulocityApi:
 
     def __enter__(self) -> MultiTenantCumulocityApp:
         return self
+
+    def __exit__(self, __exc_type, __exc_value, __traceback):
+        pass
diff --git a/c8y_api/model/_base.py b/c8y_api/model/_base.py
index c7f9e50..f1a7785 100644
--- a/c8y_api/model/_base.py
+++ b/c8y_api/model/_base.py
@@ -7,15 +7,13 @@
 from __future__ import annotations
 
 import logging
-from urllib.parse import quote_plus
 from typing import Any, Iterable, Set
+from urllib.parse import quote_plus, urlencode
 
 from collections.abc import MutableMapping
 from deprecated import deprecated
-from urllib.parse import urlencode
 
 from c8y_api._base_api import CumulocityRestApi
-
 from c8y_api.model._util import _DateUtil, _StringUtil, _QueryUtil
 
 
diff --git a/c8y_api/model/inventory.py b/c8y_api/model/inventory.py
index d069146..d54232a 100644
--- a/c8y_api/model/inventory.py
+++ b/c8y_api/model/inventory.py
@@ -8,7 +8,6 @@
 from __future__ import annotations
 
 from typing import Any, Generator, List
-from urllib.parse import urlencode, quote_plus
 
 from c8y_api.model._base import CumulocityResource
 from c8y_api.model._util import _QueryUtil
diff --git a/c8y_api/model/measurements.py b/c8y_api/model/measurements.py
index f2c07bd..24addc6 100644
--- a/c8y_api/model/measurements.py
+++ b/c8y_api/model/measurements.py
@@ -9,7 +9,6 @@
 import dataclasses
 from datetime import datetime, timedelta
 from typing import Type, List, Generator, Sequence
-from urllib.parse import urlencode, quote_plus
 
 from c8y_api._base_api import CumulocityRestApi
 
diff --git a/c8y_tk/interactive/context.py b/c8y_tk/interactive/context.py
index d98d00f..4f04959 100644
--- a/c8y_tk/interactive/context.py
+++ b/c8y_tk/interactive/context.py
@@ -3,7 +3,6 @@
 # and/or its subsidiaries and/or its affiliates and/or their licensors.
 # Use, reproduction, transfer, publication or disclosure is prohibited except
 # as specifically provided for in your License Agreement with Software AG.
-import contextlib
 # pylint: disable=protected-access
 
 import getpass
diff --git a/integration_tests/test_apps.py b/integration_tests/test_apps.py
index b2b1369..6881a92 100644
--- a/integration_tests/test_apps.py
+++ b/integration_tests/test_apps.py
@@ -103,4 +103,4 @@ def test_context_manager(test_environment):
         assert c8y.username
 
     with MultiTenantCumulocityApp() as c8y:
-        assert c8y.username
+        assert c8y.bootstrap_instance.username
diff --git a/integration_tests/test_measurements.py b/integration_tests/test_measurements.py
index e0ec505..2e3caa9 100644
--- a/integration_tests/test_measurements.py
+++ b/integration_tests/test_measurements.py
@@ -66,6 +66,7 @@ def factory_fun(n: int, device=None, type=None, series=None) -> List[Measurement
 
 def test_select(live_c8y: CumulocityApi, measurement_factory):
     """Verify that selection works as expected."""
+    # pylint: disable=too-many-statements)
     logging.basicConfig()
     logging.getLogger().setLevel(logging.DEBUG)
     requests_log = logging.getLogger("requests.packages.urllib3")
@@ -77,21 +78,17 @@ def test_select(live_c8y: CumulocityApi, measurement_factory):
 
     # create a couple of measurements (at a new device)
     created_ms = measurement_factory(10, type=name, series=name)
-    created_values = [m[name]['series'].value for m in created_ms]
 
     # create a couple of measurements with different source
     source_ms = measurement_factory(10, type=name, series=name)
-    source_values = [m[name]['series'].value for m in source_ms]
 
     # create a couple of measurements with different type name
     device_id = created_ms[0].source
     device = live_c8y.device_inventory.get(created_ms[0].source)
     type_ms = measurement_factory(10, device=device, type=other_name, series=name)
-    type_values = [m[name]['series'].value for m in type_ms]
 
     # create a couple of measurements with different series name
     series_ms = measurement_factory(10, device=device, type=name, series=other_name)
-    series_values = [m[other_name]['series'].value for m in series_ms]
 
     # (1) all measurement collections can be selected separately
 
diff --git a/tests/model/test_base.py b/tests/model/test_base.py
index 883761d..2a7172e 100644
--- a/tests/model/test_base.py
+++ b/tests/model/test_base.py
@@ -247,11 +247,11 @@ def test_iteration(page_size, num_all, limit, expected):
     all_items = [{'i': i} for i in range(num_all)]
 
     # returns a 'page' from all items
-    def get_page(_, page):
+    def get_page(_, p):
         nonlocal all_items
-        s = page_size * (page - 1)
-        e = page_size * page
-        return [i for i in all_items[s:e]]
+        s = page_size * (p - 1)
+        e = page_size * p
+        return all_items[s:e]
 
     # parses an item as CumulocityObject
     def parse_fun(item):
@@ -261,7 +261,7 @@ def parse_fun(item):
 
     # create class under test
     res = CumulocityResource(Mock(CumulocityRestApi), '')
-    res._get_page = get_page
+    res._get_page = Mock(side_effect=get_page)
 
     # iterate oder results
     result = list(res._iterate(base_query="q", page_number=None, limit=limit, parse_fun=parse_fun))
diff --git a/tests/model/test_inventory.py b/tests/model/test_inventory.py
index e06795c..444346e 100644
--- a/tests/model/test_inventory.py
+++ b/tests/model/test_inventory.py
@@ -4,7 +4,7 @@
 # Use, reproduction, transfer, publication or disclosure is prohibited except
 # as specifically provided for in your License Agreement with Software AG.
 # pylint: disable=protected-access
-import itertools
+
 from unittest.mock import Mock
 
 import pytest
@@ -108,6 +108,7 @@ def _invoke_target_and_isolate_url(target, kwargs):
 
 
 def gen_common_select_cases():
+    """Generate test case data for common select cases."""
     return [
         # expression has the highest priority
         ({'expression': 'EX', 'query': 'QUERY'}, ['?EX'], ['query=', 'QUERY']),
@@ -156,6 +157,7 @@ def gen_common_select_cases():
 
 
 def gen_common_select_cases_ids():
+    """Generate test case ID for common select cases."""
     return ['+'.join(x[0].keys()) for x in gen_common_select_cases()]
 
 
@@ -171,6 +173,7 @@ def gen_common_select_cases_ids():
         'group_inventory.get_count',
 ])
 def test_common_select_params(fun, params, expected, not_expected):
+    """Verify that common select parameters are handled correctly."""
     url = _invoke_target_and_isolate_url(fun, params)
     for e in expected:
         assert e in url
diff --git a/tests/model/test_operations.py b/tests/model/test_operations.py
index 8288455..5eb3b99 100644
--- a/tests/model/test_operations.py
+++ b/tests/model/test_operations.py
@@ -5,14 +5,13 @@
 # as specifically provided for in your License Agreement with Software AG.
 
 from datetime import timedelta
-from unittest.mock import Mock, patch
+from unittest.mock import Mock
 from urllib.parse import unquote_plus
 
 import pytest
 
 from c8y_api import CumulocityApi
 from c8y_api.model import Operations
-from model import BulkOperations
 
 from tests.utils import isolate_last_call_arg