diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5d47c3971..c5df40835 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,9 @@
 # Changelog
 
+## Ongoing
+
+- Implement async file-open in tests
+
 ## v1.7.6
 
 - Maintenance chores (mostly reworking Github CI Actions) backporting from efforts on Python Plugwise [USB: #264](https://github.com/plugwise/python-plugwise-usb/pull/264) after porting our progress using [USB: #263](https://github.com/plugwise/python-plugwise-usb/pull/263)
diff --git a/pyproject.toml b/pyproject.toml
index ede4e456a..ef4299677 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -25,6 +25,7 @@ maintainers = [
 ]
 requires-python = ">=3.13"
 dependencies    = [
+        "aiofiles",
         "aiohttp",
         "defusedxml",
         "munch",
diff --git a/tests/test_adam.py b/tests/test_adam.py
index 96b015ce5..1ef41c0de 100644
--- a/tests/test_adam.py
+++ b/tests/test_adam.py
@@ -21,7 +21,7 @@ async def test_connect_adam_plus_anna_new(self):
         """Test extended Adam (firmware 3.7) with Anna and a switch-group setup."""
         self.smile_setup = "adam_plus_anna_new"
 
-        testdata = self.load_testdata(SMILE_TYPE, self.smile_setup)
+        testdata = await self.load_testdata(SMILE_TYPE, self.smile_setup)
         server, smile, client = await self.connect_wrapper()
         assert smile.smile_hostname == "smile000000"
 
@@ -139,7 +139,7 @@ async def test_connect_adam_plus_anna_new(self):
 
         # Now change some data and change directory reading xml from
         # emulating reading newer dataset after an update_interval
-        testdata_updated = self.load_testdata(
+        testdata_updated = await self.load_testdata(
             SMILE_TYPE, f"{self.smile_setup}_UPDATED_DATA"
         )
         self.smile_setup = "updated/adam_plus_anna_new"
@@ -167,7 +167,7 @@ async def test_connect_adam_plus_anna_new(self):
         await self.disconnect(server, client)
 
         self.smile_setup = "adam_plus_anna_new"
-        testdata = self.load_testdata(SMILE_TYPE, self.smile_setup)
+        testdata = await self.load_testdata(SMILE_TYPE, self.smile_setup)
         server, smile, client = await self.connect_wrapper(raise_timeout=True)
         await self.device_test(
             smile, "2023-12-17 00:00:01", testdata, skip_testing=True
@@ -190,7 +190,7 @@ async def test_connect_adam_plus_anna_new_regulation_off(self):
         """Test regultaion_mode off with control_state key missing for Adam."""
         self.smile_setup = "adam_plus_anna_new_regulation_off"
 
-        testdata = self.load_testdata(SMILE_TYPE, self.smile_setup)
+        testdata = await self.load_testdata(SMILE_TYPE, self.smile_setup)
         server, smile, client = await self.connect_wrapper()
         assert smile.smile_hostname == "smile000000"
 
@@ -204,7 +204,7 @@ async def test_connect_adam_zone_per_device(self):
         """Test an extensive setup of Adam with a zone per device."""
         self.smile_setup = "adam_zone_per_device"
 
-        testdata = self.load_testdata(SMILE_TYPE, self.smile_setup)
+        testdata = await self.load_testdata(SMILE_TYPE, self.smile_setup)
         server, smile, client = await self.connect_wrapper()
         assert smile.smile_hostname == "smile000000"
 
@@ -285,7 +285,7 @@ async def test_connect_adam_multiple_devices_per_zone(self):
         """Test an extensive setup of Adam with multiple devices per zone."""
         self.smile_setup = "adam_multiple_devices_per_zone"
 
-        testdata = self.load_testdata(SMILE_TYPE, self.smile_setup)
+        testdata = await self.load_testdata(SMILE_TYPE, self.smile_setup)
         server, smile, client = await self.connect_wrapper()
         assert smile.smile_hostname == "smile000000"
 
@@ -333,7 +333,7 @@ async def test_adam_heatpump_cooling(self):
         """Test Adam with heatpump in cooling mode and idle."""
         self.smile_setup = "adam_heatpump_cooling"
 
-        testdata = self.load_testdata(SMILE_TYPE, self.smile_setup)
+        testdata = await self.load_testdata(SMILE_TYPE, self.smile_setup)
         server, smile, client = await self.connect_wrapper()
 
         await self.device_test(smile, "2022-01-02 00:00:01", testdata)
@@ -359,7 +359,7 @@ async def test_connect_adam_onoff_cooling_fake_firmware(self):
         """Test an Adam with a fake OnOff cooling device in cooling mode."""
         self.smile_setup = "adam_onoff_cooling_fake_firmware"
 
-        testdata = self.load_testdata(SMILE_TYPE, self.smile_setup)
+        testdata = await self.load_testdata(SMILE_TYPE, self.smile_setup)
         server, smile, client = await self.connect_wrapper()
         assert smile.smile_hostname == "smile000000"
 
@@ -382,7 +382,7 @@ async def test_connect_adam_plus_anna(self):
         """Test Adam (firmware 3.0) with Anna setup."""
         self.smile_setup = "adam_plus_anna"
 
-        testdata = self.load_testdata(SMILE_TYPE, self.smile_setup)
+        testdata = await self.load_testdata(SMILE_TYPE, self.smile_setup)
         server, smile, client = await self.connect_wrapper()
         assert smile.smile_hostname == "smile000000"
 
@@ -432,7 +432,7 @@ async def test_adam_plus_jip(self):
         """Test Adam with Jip setup."""
         self.smile_setup = "adam_jip"
 
-        testdata = self.load_testdata(SMILE_TYPE, self.smile_setup)
+        testdata = await self.load_testdata(SMILE_TYPE, self.smile_setup)
         server, smile, client = await self.connect_wrapper()
 
         await self.device_test(smile, "2021-06-20 00:00:01", testdata)
diff --git a/tests/test_anna.py b/tests/test_anna.py
index bce21b1ab..92efae3d9 100644
--- a/tests/test_anna.py
+++ b/tests/test_anna.py
@@ -17,7 +17,7 @@ async def test_connect_anna_v4(self):
         """Test an Anna firmware 4 setup."""
         self.smile_setup = "anna_v4"
 
-        testdata = self.load_testdata(SMILE_TYPE, self.smile_setup)
+        testdata = await self.load_testdata(SMILE_TYPE, self.smile_setup)
         server, smile, client = await self.connect_wrapper()
         assert smile.smile_hostname == "smile000000"
 
@@ -55,7 +55,7 @@ async def test_connect_anna_v4(self):
 
         # Now change some data and change directory reading xml from
         # emulating reading newer dataset after an update_interval
-        testdata_updated = self.load_testdata(
+        testdata_updated = await self.load_testdata(
             SMILE_TYPE, f"{self.smile_setup}_UPDATED_DATA"
         )
 
@@ -97,7 +97,7 @@ async def test_connect_anna_v4_dhw(self):
         """Test an Anna firmware 4 setup for domestic hot water."""
         self.smile_setup = "anna_v4_dhw"
 
-        testdata = self.load_testdata(SMILE_TYPE, self.smile_setup)
+        testdata = await self.load_testdata(SMILE_TYPE, self.smile_setup)
         server, smile, client = await self.connect_wrapper()
         assert smile.smile_hostname == "smile000000"
 
@@ -127,7 +127,7 @@ async def test_connect_anna_v4_no_tag(self):
         """Test an Anna firmware 4 setup - missing tag (issue)."""
         self.smile_setup = "anna_v4_no_tag"
 
-        testdata = self.load_testdata(SMILE_TYPE, self.smile_setup)
+        testdata = await self.load_testdata(SMILE_TYPE, self.smile_setup)
         server, smile, client = await self.connect_wrapper()
         assert smile.smile_hostname == "smile000000"
 
@@ -155,7 +155,7 @@ async def test_connect_anna_without_boiler_fw441(self):
         """Test an Anna with firmware 4.4, without a boiler."""
         self.smile_setup = "anna_without_boiler_fw441"
 
-        testdata = self.load_testdata(SMILE_TYPE, self.smile_setup)
+        testdata = await self.load_testdata(SMILE_TYPE, self.smile_setup)
         server, smile, client = await self.connect_wrapper()
         assert smile.smile_hostname == "smile000000"
 
@@ -183,7 +183,7 @@ async def test_connect_anna_heatpump_heating(self):
 
         self.smile_setup = "anna_heatpump_heating"
 
-        testdata = self.load_testdata(SMILE_TYPE, self.smile_setup)
+        testdata = await self.load_testdata(SMILE_TYPE, self.smile_setup)
         server, smile, client = await self.connect_wrapper()
         assert smile.smile_hostname == "smile000000"
 
@@ -218,7 +218,7 @@ async def test_connect_anna_heatpump_heating(self):
         # Now change some data and change directory reading xml from
         # emulating reading newer dataset after an update_interval,
         # set testday to Monday to force an incremental update
-        testdata_updated = self.load_testdata(
+        testdata_updated = await self.load_testdata(
             SMILE_TYPE, f"{self.smile_setup}_UPDATED_DATA"
         )
 
@@ -240,7 +240,7 @@ async def test_connect_anna_heatpump_cooling(self):
         """
         self.smile_setup = "anna_heatpump_cooling"
 
-        testdata = self.load_testdata(SMILE_TYPE, self.smile_setup)
+        testdata = await self.load_testdata(SMILE_TYPE, self.smile_setup)
         server, smile, client = await self.connect_wrapper()
         assert smile.smile_hostname == "smile000000"
 
@@ -287,7 +287,7 @@ async def test_connect_anna_heatpump_cooling_fake_firmware(self):
         """
         self.smile_setup = "anna_heatpump_cooling_fake_firmware"
 
-        testdata = self.load_testdata(SMILE_TYPE, self.smile_setup)
+        testdata = await self.load_testdata(SMILE_TYPE, self.smile_setup)
         server, smile, client = await self.connect_wrapper()
         assert smile.smile_hostname == "smile000000"
 
@@ -312,7 +312,7 @@ async def test_connect_anna_elga_no_cooling(self):
 
         self.smile_setup = "anna_elga_no_cooling"
 
-        testdata = self.load_testdata(SMILE_TYPE, self.smile_setup)
+        testdata = await self.load_testdata(SMILE_TYPE, self.smile_setup)
         server, smile, client = await self.connect_wrapper()
         assert smile.smile_hostname == "smile000000"
 
@@ -337,7 +337,7 @@ async def test_connect_anna_elga_2(self):
         """Test a 2nd Anna with Elga setup, cooling off, in idle mode (with missing outdoor temperature - solved)."""
         self.smile_setup = "anna_elga_2"
 
-        testdata = self.load_testdata(SMILE_TYPE, self.smile_setup)
+        testdata = await self.load_testdata(SMILE_TYPE, self.smile_setup)
         server, smile, client = await self.connect_wrapper()
         assert smile.smile_hostname == "smile000000"
 
@@ -366,7 +366,7 @@ async def test_connect_anna_elga_2_schedule_off(self):
         """Test Anna with Elga setup, cooling off, in idle mode, modified to schedule off."""
         self.smile_setup = "anna_elga_2_schedule_off"
 
-        testdata = self.load_testdata(SMILE_TYPE, self.smile_setup)
+        testdata = await self.load_testdata(SMILE_TYPE, self.smile_setup)
         server, smile, client = await self.connect_wrapper()
         assert smile.smile_hostname == "smile000000"
 
@@ -391,7 +391,7 @@ async def test_connect_anna_elga_2_cooling(self):
         """
         self.smile_setup = "anna_elga_2_cooling"
 
-        testdata = self.load_testdata(SMILE_TYPE, self.smile_setup)
+        testdata = await self.load_testdata(SMILE_TYPE, self.smile_setup)
         server, smile, client = await self.connect_wrapper()
         assert smile.smile_hostname == "smile000000"
 
@@ -421,7 +421,7 @@ async def test_connect_anna_elga_2_cooling(self):
         assert result
 
         # Simulate a change of season: from cooling to heating after an update_interval
-        testdata_updated = self.load_testdata(
+        testdata_updated = await self.load_testdata(
             SMILE_TYPE, f"{self.smile_setup}_UPDATED_DATA"
         )
 
@@ -448,7 +448,7 @@ async def test_connect_anna_loria_heating_idle(self):
         """Test an Anna with a Loria in heating mode - state idle."""
         self.smile_setup = "anna_loria_heating_idle"
 
-        testdata = self.load_testdata(SMILE_TYPE, self.smile_setup)
+        testdata = await self.load_testdata(SMILE_TYPE, self.smile_setup)
         server, smile, client = await self.connect_wrapper()
         assert smile.smile_hostname == "smile000000"
 
@@ -516,7 +516,7 @@ async def test_connect_anna_loria_cooling_active(self):
         """Test an Anna with a Loria in heating mode - state idle."""
         self.smile_setup = "anna_loria_cooling_active"
 
-        testdata = self.load_testdata(SMILE_TYPE, self.smile_setup)
+        testdata = await self.load_testdata(SMILE_TYPE, self.smile_setup)
         server, smile, client = await self.connect_wrapper()
         assert smile.smile_hostname == "smile000000"
 
@@ -540,7 +540,7 @@ async def test_connect_anna_loria_driessens(self):
         """Test an Anna with a Loria in heating mode - state idle."""
         self.smile_setup = "anna_loria_driessens"
 
-        testdata = self.load_testdata(SMILE_TYPE, self.smile_setup)
+        testdata = await self.load_testdata(SMILE_TYPE, self.smile_setup)
         server, smile, client = await self.connect_wrapper()
         assert smile.smile_hostname == "smile000000"
 
diff --git a/tests/test_init.py b/tests/test_init.py
index c80468ec6..ed6be9ece 100644
--- a/tests/test_init.py
+++ b/tests/test_init.py
@@ -16,6 +16,7 @@
 import pytest
 
 # Testing
+import aiofiles
 import aiohttp
 from freezegun import freeze_time
 from packaging import version
@@ -50,7 +51,7 @@
 class TestPlugwise:  # pylint: disable=attribute-defined-outside-init
     """Tests for Plugwise Smile."""
 
-    def _write_json(self, call, data):
+    async def _write_json(self, call, data):
         """Store JSON data to per-setup files for HA component testing."""
         no_fixtures = os.getenv("NO_FIXTURES") == "1"
         if no_fixtures:
@@ -65,8 +66,8 @@ def _write_json(self, call, data):
         if not os.path.exists(os.path.dirname(datafile)):  # pragma: no cover
             os.mkdir(os.path.dirname(datafile))
 
-        with open(datafile, "w", encoding="utf-8") as fixture_file:
-            fixture_file.write(
+        async with aiofiles.open(datafile, "w", encoding="utf-8") as fixture_file:
+            await fixture_file.write(
                 json.dumps(
                     data,
                     indent=2,
@@ -77,15 +78,16 @@ def _write_json(self, call, data):
                 + "\n"
             )
 
-    def load_testdata(
+    async def load_testdata(
         self, smile_type: str = "adam", smile_setup: str = "adam_zone_per_device"
     ):
         """Load JSON data from setup, return as object."""
         path = os.path.join(
             os.path.dirname(__file__), f"../tests/data/{smile_type}/{smile_setup}.json"
         )
-        with open(path, encoding="utf-8") as testdata_file:
-            return json.load(testdata_file)
+        async with aiofiles.open(path, encoding="utf-8") as testdata_file:
+            content = await testdata_file.read()
+            return json.loads(content)
 
     async def setup_app(
         self,
@@ -187,8 +189,8 @@ async def smile_appliances(self, request):
             os.path.dirname(__file__),
             f"../userdata/{self.smile_setup}/core.appliances.xml",
         )
-        with open(userdata, encoding="utf-8") as filedata:
-            data = filedata.read()
+        async with aiofiles.open(userdata, encoding="utf-8") as filedata:
+            data = await filedata.read()
         return aiohttp.web.Response(text=data)
 
     async def smile_domain_objects(self, request):
@@ -197,8 +199,8 @@ async def smile_domain_objects(self, request):
             os.path.dirname(__file__),
             f"../userdata/{self.smile_setup}/core.domain_objects.xml",
         )
-        with open(userdata, encoding="utf-8") as filedata:
-            data = filedata.read()
+        async with aiofiles.open(userdata, encoding="utf-8") as filedata:
+            data = await filedata.read()
         return aiohttp.web.Response(text=data)
 
     async def smile_locations(self, request):
@@ -207,8 +209,8 @@ async def smile_locations(self, request):
             os.path.dirname(__file__),
             f"../userdata/{self.smile_setup}/core.locations.xml",
         )
-        with open(userdata, encoding="utf-8") as filedata:
-            data = filedata.read()
+        async with aiofiles.open(userdata, encoding="utf-8") as filedata:
+            data = await filedata.read()
         return aiohttp.web.Response(text=data)
 
     async def smile_modules(self, request):
@@ -217,8 +219,8 @@ async def smile_modules(self, request):
             os.path.dirname(__file__),
             f"../userdata/{self.smile_setup}/core.modules.xml",
         )
-        with open(userdata, encoding="utf-8") as filedata:
-            data = filedata.read()
+        async with aiofiles.open(userdata, encoding="utf-8") as filedata:
+            data = await filedata.read()
         return aiohttp.web.Response(text=data)
 
     async def smile_status(self, request):
@@ -228,8 +230,8 @@ async def smile_status(self, request):
                 os.path.dirname(__file__),
                 f"../userdata/{self.smile_setup}/system_status_xml.xml",
             )
-            with open(userdata, encoding="utf-8") as filedata:
-                data = filedata.read()
+            async with aiofiles.open(userdata, encoding="utf-8") as filedata:
+                data = await filedata.read()
             return aiohttp.web.Response(text=data)
         except OSError as exc:
             raise aiohttp.web.HTTPNotFound from exc
@@ -641,7 +643,7 @@ def test_and_assert(test_dict, data, header):
                         "cooling_state"
                     ]
 
-        self._write_json("data", data)
+        await self._write_json("data", data)
 
         if "FIXTURES" in os.environ:
             _LOGGER.info("Skipping tests: Requested fixtures only")  # pragma: no cover
diff --git a/tests/test_legacy_anna.py b/tests/test_legacy_anna.py
index a3a7b8469..1a2e7e20f 100644
--- a/tests/test_legacy_anna.py
+++ b/tests/test_legacy_anna.py
@@ -16,7 +16,7 @@ class TestPlugwiseAnna(TestPlugwise):  # pylint: disable=attribute-defined-outsi
     async def test_connect_legacy_anna(self):
         """Test a legacy Anna device."""
         self.smile_setup = "legacy_anna"
-        testdata = self.load_testdata(SMILE_TYPE, self.smile_setup)
+        testdata = await self.load_testdata(SMILE_TYPE, self.smile_setup)
 
         server, smile, client = await self.connect_legacy_wrapper()
         assert smile.smile_hostname == "smile000000"
@@ -53,7 +53,7 @@ async def test_connect_legacy_anna_2(self):
         """Test another legacy Anna device."""
         self.smile_setup = "legacy_anna_2"
 
-        testdata = self.load_testdata(SMILE_TYPE, self.smile_setup)
+        testdata = await self.load_testdata(SMILE_TYPE, self.smile_setup)
         server, smile, client = await self.connect_legacy_wrapper()
         assert smile.smile_hostname == "smile000000"
 
diff --git a/tests/test_legacy_p1.py b/tests/test_legacy_p1.py
index d569ca52b..52f1d8504 100644
--- a/tests/test_legacy_p1.py
+++ b/tests/test_legacy_p1.py
@@ -15,7 +15,7 @@ async def test_connect_smile_p1_v2(self):
         """Test a legacy P1 device."""
         self.smile_setup = "smile_p1_v2"
 
-        testdata = self.load_testdata(SMILE_TYPE, self.smile_setup)
+        testdata = await self.load_testdata(SMILE_TYPE, self.smile_setup)
         server, smile, client = await self.connect_legacy_wrapper()
         assert smile.smile_hostname == "smile000000"
 
@@ -39,7 +39,7 @@ async def test_connect_smile_p1_v2_2(self):
         """Test another legacy P1 device."""
         self.smile_setup = "smile_p1_v2_2"
 
-        testdata = self.load_testdata(SMILE_TYPE, self.smile_setup)
+        testdata = await self.load_testdata(SMILE_TYPE, self.smile_setup)
         server, smile, client = await self.connect_legacy_wrapper()
         assert smile.smile_hostname == "smile000000"
 
@@ -56,7 +56,7 @@ async def test_connect_smile_p1_v2_2(self):
 
         # Now change some data and change directory reading xml from
         # emulating reading newer dataset after an update_interval
-        testdata_updated = self.load_testdata(
+        testdata_updated = await self.load_testdata(
             SMILE_TYPE, f"{self.smile_setup}_UPDATED_DATA"
         )
         self.smile_setup = "updated/smile_p1_v2_2"
diff --git a/tests/test_legacy_stretch.py b/tests/test_legacy_stretch.py
index 021cc385b..13d079020 100644
--- a/tests/test_legacy_stretch.py
+++ b/tests/test_legacy_stretch.py
@@ -15,7 +15,7 @@ async def test_connect_stretch_v31(self):
         """Test a legacy Stretch with firmware 3.1 setup."""
         self.smile_setup = "stretch_v31"
 
-        testdata = self.load_testdata(SMILE_TYPE, self.smile_setup)
+        testdata = await self.load_testdata(SMILE_TYPE, self.smile_setup)
         server, smile, client = await self.connect_legacy_wrapper(stretch=True)
         assert smile.smile_hostname == "stretch000000"
 
@@ -39,7 +39,7 @@ async def test_connect_stretch_v31(self):
 
         # Now change some data and change directory reading xml from
         # emulating reading newer dataset after an update_interval
-        testdata_updated = self.load_testdata(
+        testdata_updated = await self.load_testdata(
             SMILE_TYPE, f"{self.smile_setup}_UPDATED_DATA"
         )
         self.smile_setup = "updated/stretch_v31"
@@ -55,7 +55,7 @@ async def test_connect_stretch_v23(self):
         """Test a legacy Stretch with firmware 2.3 setup."""
         self.smile_setup = "stretch_v23"
 
-        testdata = self.load_testdata(SMILE_TYPE, self.smile_setup)
+        testdata = await self.load_testdata(SMILE_TYPE, self.smile_setup)
         server, smile, client = await self.connect_legacy_wrapper(stretch=True)
         assert smile.smile_hostname == "stretch000000"
 
@@ -94,7 +94,7 @@ async def test_connect_stretch_v27_no_domain(self):
         # testdata dictionary with key ctrl_id_dev_id => keys:values
         self.smile_setup = "stretch_v27_no_domain"
 
-        testdata = self.load_testdata(SMILE_TYPE, self.smile_setup)
+        testdata = await self.load_testdata(SMILE_TYPE, self.smile_setup)
         server, smile, client = await self.connect_legacy_wrapper(stretch=True)
         assert smile.smile_hostname == "stretch000000"
 
diff --git a/tests/test_p1.py b/tests/test_p1.py
index 562ebc4fd..e379573e6 100644
--- a/tests/test_p1.py
+++ b/tests/test_p1.py
@@ -15,7 +15,7 @@ async def test_connect_p1v4_442_single(self):
         """Test a P1 firmware 4.4 single-phase setup."""
         self.smile_setup = "p1v4_442_single"
 
-        testdata = self.load_testdata(SMILE_TYPE, self.smile_setup)
+        testdata = await self.load_testdata(SMILE_TYPE, self.smile_setup)
         server, smile, client = await self.connect_wrapper()
         assert smile.smile_hostname == "smile000000"
 
@@ -33,7 +33,7 @@ async def test_connect_p1v4_442_single(self):
 
         # Now change some data and change directory reading xml from
         # emulating reading newer dataset after an update_interval
-        testdata_updated = self.load_testdata(
+        testdata_updated = await self.load_testdata(
             SMILE_TYPE, f"{self.smile_setup}_UPDATED_DATA"
         )
         self.smile_setup = "updated/p1v4_442_single"
@@ -65,7 +65,7 @@ async def test_connect_p1v4_442_triple(self):
         """Test a P1 firmware 4 3-phase setup."""
         self.smile_setup = "p1v4_442_triple"
 
-        testdata = self.load_testdata(SMILE_TYPE, self.smile_setup)
+        testdata = await self.load_testdata(SMILE_TYPE, self.smile_setup)
         server, smile, client = await self.connect_wrapper()
         assert smile.smile_hostname == "smile000000"