diff --git a/lib/iris/tests/_shared_utils.py b/lib/iris/tests/_shared_utils.py
index 3f1aba3398..4a0d275cdd 100644
--- a/lib/iris/tests/_shared_utils.py
+++ b/lib/iris/tests/_shared_utils.py
@@ -19,7 +19,7 @@
 import re
 import shutil
 import subprocess
-from typing import AnyStr
+from typing import Optional
 import warnings
 import xml.dom.minidom
 import zlib
@@ -380,7 +380,7 @@ def sort_key(line):
 
     dimension_lines = slice(lines.index("dimensions:") + 1, lines.index("variables:"))
     lines[dimension_lines] = sorted(lines[dimension_lines], key=sort_key)
-    cdl = "\n".join(lines) + "\n"
+    cdl = "\n".join(lines) + "\n"  # type: ignore[assignment]
 
     _check_same(cdl, reference_path, type_comparison_name="CDL")
 
@@ -543,9 +543,7 @@ def assert_repr(request: pytest.FixtureRequest, obj, reference_filename):
 def _check_same(item, reference_path, type_comparison_name="CML"):
     if _check_reference_file(reference_path):
         with open(reference_path, "rb") as reference_fh:
-            reference = "".join(
-                part.decode("utf-8") for part in reference_fh.readlines()
-            )
+            reference = "".join(part.decode("utf-8") for part in reference_fh)
         _assert_str_same(reference, item, reference_path, type_comparison_name)
     else:
         _ensure_folder(reference_path)
@@ -966,7 +964,7 @@ def wrapped(*args, **kwargs):
     return wrapped
 
 
-def env_bin_path(exe_name: AnyStr = None):
+def env_bin_path(exe_name: Optional[str] = None):
     """Return a Path object for (an executable in) the environment bin directory.
 
     Parameters
diff --git a/lib/iris/tests/conftest.py b/lib/iris/tests/conftest.py
index c75e1ae71c..2a3341d8c0 100644
--- a/lib/iris/tests/conftest.py
+++ b/lib/iris/tests/conftest.py
@@ -9,6 +9,7 @@
 """
 
 from collections import defaultdict
+from typing import Callable
 
 import pytest
 
@@ -27,7 +28,7 @@ def test_call_counter():
 
 
 @pytest.fixture
-def _unique_id(request: pytest.FixtureRequest, test_call_counter) -> callable:
+def _unique_id(request: pytest.FixtureRequest, test_call_counter) -> Callable:
     """Provide a function returning a unique ID of calling test and call number.
 
     Example: ``iris.tests.unit.test_cube.TestCube.test_data.my_param.0``
diff --git a/lib/iris/tests/graphics/__init__.py b/lib/iris/tests/graphics/__init__.py
index 7855f6a037..7fb2074ca0 100644
--- a/lib/iris/tests/graphics/__init__.py
+++ b/lib/iris/tests/graphics/__init__.py
@@ -18,7 +18,7 @@
 from pathlib import Path
 import sys
 import threading
-from typing import Callable, Dict, Union
+from typing import Callable, Dict, Iterator, Union
 
 import filelock
 import pytest
@@ -285,7 +285,7 @@ def skip_plot(fn: Callable) -> Callable:
 
 
 @pytest.fixture
-def _check_graphic_caller(_unique_id) -> callable:
+def _check_graphic_caller(_unique_id) -> Iterator[Callable]:
     """Provide a function calling :func:`check_graphic` with safe configuration.
 
     Ensures a safe Matplotlib setup (and tears down afterwards), and generates
diff --git a/lib/iris/tests/integration/plot/test_animate.py b/lib/iris/tests/integration/plot/test_animate.py
index 9008a53b84..59f269e9f7 100644
--- a/lib/iris/tests/integration/plot/test_animate.py
+++ b/lib/iris/tests/integration/plot/test_animate.py
@@ -3,6 +3,7 @@
 # This file is part of Iris and is released under the BSD license.
 # See LICENSE in the root of the repository for full licensing details.
 """Integration tests for :func:`iris.plot.animate`."""
+
 import numpy as np
 import pytest
 
diff --git a/lib/iris/tests/integration/plot/test_colorbar.py b/lib/iris/tests/integration/plot/test_colorbar.py
index a1d498f200..e02e51db78 100644
--- a/lib/iris/tests/integration/plot/test_colorbar.py
+++ b/lib/iris/tests/integration/plot/test_colorbar.py
@@ -6,6 +6,7 @@
 :func:`matplotlib.pyplot.colorbar`.
 
 """
+
 import numpy as np
 import pytest
 
diff --git a/lib/iris/tests/integration/plot/test_netcdftime.py b/lib/iris/tests/integration/plot/test_netcdftime.py
index 9c1d4cf5e6..408c04cb3b 100644
--- a/lib/iris/tests/integration/plot/test_netcdftime.py
+++ b/lib/iris/tests/integration/plot/test_netcdftime.py
@@ -3,6 +3,7 @@
 # This file is part of Iris and is released under the BSD license.
 # See LICENSE in the root of the repository for full licensing details.
 """Test plot of time coord with non-standard calendar."""
+
 from cf_units import Unit
 import cftime
 import numpy as np
diff --git a/lib/iris/tests/integration/plot/test_plot_2d_coords.py b/lib/iris/tests/integration/plot/test_plot_2d_coords.py
index 1b3c850bbe..f4e23fad7b 100644
--- a/lib/iris/tests/integration/plot/test_plot_2d_coords.py
+++ b/lib/iris/tests/integration/plot/test_plot_2d_coords.py
@@ -4,7 +4,6 @@
 # See LICENSE in the root of the repository for full licensing details.
 """Test plots with two dimensional coordinates."""
 
-
 import cartopy.crs as ccrs
 import matplotlib.pyplot as plt
 import numpy as np
diff --git a/lib/iris/tests/unit/common/metadata/test_CubeMetadata.py b/lib/iris/tests/unit/common/metadata/test_CubeMetadata.py
index c678a285d9..0b4725da42 100644
--- a/lib/iris/tests/unit/common/metadata/test_CubeMetadata.py
+++ b/lib/iris/tests/unit/common/metadata/test_CubeMetadata.py
@@ -6,11 +6,8 @@
 
 # Import iris.tests first so that some things can be initialised before
 # importing anything else.
-from typing import Any, ClassVar
-
-from copy import deepcopy
-
 from copy import deepcopy
+from typing import Any, ClassVar
 
 import pytest
 
diff --git a/lib/iris/tests/unit/concatenate/test_concatenate.py b/lib/iris/tests/unit/concatenate/test_concatenate.py
index 9521c3af48..448ffb5e7b 100644
--- a/lib/iris/tests/unit/concatenate/test_concatenate.py
+++ b/lib/iris/tests/unit/concatenate/test_concatenate.py
@@ -51,7 +51,6 @@ def test_concat_1d_with_same_time_units(self, simple_1d_time_cubes):
 
 
 class _MessagesMixin:
-
     @pytest.fixture()
     def placeholder(self):
         # Shim to allow sample_cubes to have identical signature in both parent and subclasses
diff --git a/lib/iris/tests/unit/fileformats/abf/test_ABFField.py b/lib/iris/tests/unit/fileformats/abf/test_ABFField.py
index 2c3cb703fe..2f06c914ca 100644
--- a/lib/iris/tests/unit/fileformats/abf/test_ABFField.py
+++ b/lib/iris/tests/unit/fileformats/abf/test_ABFField.py
@@ -3,6 +3,7 @@
 # This file is part of Iris and is released under the BSD license.
 # See LICENSE in the root of the repository for full licensing details.
 """Unit tests for the `iris.fileformats.abf.ABFField` class."""
+
 from iris.fileformats.abf import ABFField
 
 
diff --git a/lib/iris/tests/unit/fileformats/cf/test_CFGroup.py b/lib/iris/tests/unit/fileformats/cf/test_CFGroup.py
index d1efc5b0ba..3724a2f628 100644
--- a/lib/iris/tests/unit/fileformats/cf/test_CFGroup.py
+++ b/lib/iris/tests/unit/fileformats/cf/test_CFGroup.py
@@ -3,6 +3,7 @@
 # This file is part of Iris and is released under the BSD license.
 # See LICENSE in the root of the repository for full licensing details.
 """Unit tests for the :class:`iris.fileformats.cf.CFGroup` class."""
+
 from unittest.mock import MagicMock
 
 import pytest
diff --git a/lib/iris/tests/unit/fileformats/cf/test_CFReader.py b/lib/iris/tests/unit/fileformats/cf/test_CFReader.py
index 8a9aad48a0..42019bb9f8 100644
--- a/lib/iris/tests/unit/fileformats/cf/test_CFReader.py
+++ b/lib/iris/tests/unit/fileformats/cf/test_CFReader.py
@@ -3,6 +3,7 @@
 # This file is part of Iris and is released under the BSD license.
 # See LICENSE in the root of the repository for full licensing details.
 """Unit tests for the `iris.fileformats.cf.CFReader` class."""
+
 from unittest import mock
 
 import numpy as np
@@ -366,8 +367,8 @@ def _setup_class(self, mocker):
             file_format="NetCDF4", variables=self.variables, ncattrs=ncattrs
         )
 
-    # @pytest.fixture(autouse=True)
-    # def _setup(self, mocker):
+        # @pytest.fixture(autouse=True)
+        # def _setup(self, mocker):
         # Restrict the CFReader functionality to only performing
         # translations and building first level cf-groups for variables.
         mocker.patch("iris.fileformats.cf.CFReader._reset")
@@ -406,4 +407,3 @@ def test_ugrid_coords(self):
 
     def test_is_cf_ugrid_group(self):
         assert isinstance(self.cf_group, CFGroup)
-
diff --git a/lib/iris/tests/unit/fileformats/dot/test__dot_path.py b/lib/iris/tests/unit/fileformats/dot/test__dot_path.py
index c72207dfcb..679f74c51d 100644
--- a/lib/iris/tests/unit/fileformats/dot/test__dot_path.py
+++ b/lib/iris/tests/unit/fileformats/dot/test__dot_path.py
@@ -3,6 +3,7 @@
 # This file is part of Iris and is released under the BSD license.
 # See LICENSE in the root of the repository for full licensing details.
 """Unit tests for :func:`iris.fileformats.dot._dot_path`."""
+
 import os.path
 import subprocess
 
diff --git a/lib/iris/tests/unit/fileformats/name_loaders/test__build_cell_methods.py b/lib/iris/tests/unit/fileformats/name_loaders/test__build_cell_methods.py
index 6b7d576cf5..b6cf87f5a6 100644
--- a/lib/iris/tests/unit/fileformats/name_loaders/test__build_cell_methods.py
+++ b/lib/iris/tests/unit/fileformats/name_loaders/test__build_cell_methods.py
@@ -3,6 +3,7 @@
 # This file is part of Iris and is released under the BSD license.
 # See LICENSE in the root of the repository for full licensing details.
 """Unit tests for :func:`iris.fileformats.name_loaders._build_cell_methods`."""
+
 import pytest
 
 import iris.coords
diff --git a/lib/iris/tests/unit/fileformats/name_loaders/test__build_lat_lon_for_NAME_timeseries.py b/lib/iris/tests/unit/fileformats/name_loaders/test__build_lat_lon_for_NAME_timeseries.py
index ce8fbdff06..39067fdf2f 100644
--- a/lib/iris/tests/unit/fileformats/name_loaders/test__build_lat_lon_for_NAME_timeseries.py
+++ b/lib/iris/tests/unit/fileformats/name_loaders/test__build_lat_lon_for_NAME_timeseries.py
@@ -3,6 +3,7 @@
 # This file is part of Iris and is released under the BSD license.
 # See LICENSE in the root of the repository for full licensing details.
 """Unit tests for :func:`iris.analysis.name_loaders._build_lat_lon_for_NAME_timeseries`."""
+
 from iris.fileformats.name_loaders import NAMECoord, _build_lat_lon_for_NAME_timeseries
 from iris.tests._shared_utils import assert_array_equal
 
diff --git a/lib/iris/tests/unit/fileformats/name_loaders/test__calc_integration_period.py b/lib/iris/tests/unit/fileformats/name_loaders/test__calc_integration_period.py
index f94b4b4857..9b40aa47ff 100644
--- a/lib/iris/tests/unit/fileformats/name_loaders/test__calc_integration_period.py
+++ b/lib/iris/tests/unit/fileformats/name_loaders/test__calc_integration_period.py
@@ -3,6 +3,7 @@
 # This file is part of Iris and is released under the BSD license.
 # See LICENSE in the root of the repository for full licensing details.
 """Unit tests for :func:`iris.fileformats.name_loaders.__calc_integration_period`."""
+
 import datetime
 
 from iris.fileformats.name_loaders import _calc_integration_period
diff --git a/lib/iris/tests/unit/fileformats/name_loaders/test__cf_height_from_name.py b/lib/iris/tests/unit/fileformats/name_loaders/test__cf_height_from_name.py
index f2fd376614..cd32f53843 100644
--- a/lib/iris/tests/unit/fileformats/name_loaders/test__cf_height_from_name.py
+++ b/lib/iris/tests/unit/fileformats/name_loaders/test__cf_height_from_name.py
@@ -6,6 +6,7 @@
 function.
 
 """
+
 import numpy as np
 
 from iris.coords import AuxCoord
diff --git a/lib/iris/tests/unit/fileformats/name_loaders/test__generate_cubes.py b/lib/iris/tests/unit/fileformats/name_loaders/test__generate_cubes.py
index df0c1ce08d..7238b68d31 100644
--- a/lib/iris/tests/unit/fileformats/name_loaders/test__generate_cubes.py
+++ b/lib/iris/tests/unit/fileformats/name_loaders/test__generate_cubes.py
@@ -3,6 +3,7 @@
 # This file is part of Iris and is released under the BSD license.
 # See LICENSE in the root of the repository for full licensing details.
 """Unit tests for :func:`iris.analysis.name_loaders._generate_cubes`."""
+
 from datetime import datetime, timedelta
 from unittest import mock
 
diff --git a/lib/iris/tests/unit/fileformats/nimrod_load_rules/test_units.py b/lib/iris/tests/unit/fileformats/nimrod_load_rules/test_units.py
index aeee7ab3ba..5c6c59c3a1 100644
--- a/lib/iris/tests/unit/fileformats/nimrod_load_rules/test_units.py
+++ b/lib/iris/tests/unit/fileformats/nimrod_load_rules/test_units.py
@@ -3,6 +3,7 @@
 # This file is part of Iris and is released under the BSD license.
 # See LICENSE in the root of the repository for full licensing details.
 """Unit tests for the `iris.fileformats.nimrod_load_rules.units` function."""
+
 import numpy as np
 import pytest
 
diff --git a/lib/iris/tests/unit/fileformats/nimrod_load_rules/test_vertical_coord.py b/lib/iris/tests/unit/fileformats/nimrod_load_rules/test_vertical_coord.py
index 9daeb18c05..2a3d06e56a 100644
--- a/lib/iris/tests/unit/fileformats/nimrod_load_rules/test_vertical_coord.py
+++ b/lib/iris/tests/unit/fileformats/nimrod_load_rules/test_vertical_coord.py
@@ -6,6 +6,7 @@
 function.
 
 """
+
 import pytest
 
 from iris.fileformats.nimrod import NimrodField
diff --git a/lib/iris/tests/unit/fileformats/pp_load_rules/test__all_other_rules.py b/lib/iris/tests/unit/fileformats/pp_load_rules/test__all_other_rules.py
index 2220929395..05f9c6f82b 100644
--- a/lib/iris/tests/unit/fileformats/pp_load_rules/test__all_other_rules.py
+++ b/lib/iris/tests/unit/fileformats/pp_load_rules/test__all_other_rules.py
@@ -3,6 +3,7 @@
 # This file is part of Iris and is released under the BSD license.
 # See LICENSE in the root of the repository for full licensing details.
 """Unit tests for the `iris.fileformats.pp_load_rules._all_other_rules` function."""
+
 from unittest import mock
 
 from cf_units import CALENDAR_360_DAY, Unit
diff --git a/lib/iris/tests/unit/fileformats/pp_load_rules/test__collapse_degenerate_points_and_bounds.py b/lib/iris/tests/unit/fileformats/pp_load_rules/test__collapse_degenerate_points_and_bounds.py
index e666ae2d9a..523aef0e64 100644
--- a/lib/iris/tests/unit/fileformats/pp_load_rules/test__collapse_degenerate_points_and_bounds.py
+++ b/lib/iris/tests/unit/fileformats/pp_load_rules/test__collapse_degenerate_points_and_bounds.py
@@ -6,6 +6,7 @@
 :func:`iris.fileformats.pp_load_rules._collapse_degenerate_points_and_bounds`.
 
 """
+
 import numpy as np
 
 from iris.fileformats.pp_load_rules import _collapse_degenerate_points_and_bounds
diff --git a/lib/iris/tests/unit/fileformats/pp_load_rules/test__convert_scalar_pseudo_level_coords.py b/lib/iris/tests/unit/fileformats/pp_load_rules/test__convert_scalar_pseudo_level_coords.py
index 978097e8ee..ad15d7a395 100644
--- a/lib/iris/tests/unit/fileformats/pp_load_rules/test__convert_scalar_pseudo_level_coords.py
+++ b/lib/iris/tests/unit/fileformats/pp_load_rules/test__convert_scalar_pseudo_level_coords.py
@@ -6,6 +6,7 @@
 :func:`iris.fileformats.pp_load_rules._convert_pseudo_level_coords`.
 
 """
+
 from iris.coords import DimCoord
 from iris.fileformats.pp_load_rules import _convert_scalar_pseudo_level_coords
 
diff --git a/lib/iris/tests/unit/fileformats/pp_load_rules/test__convert_scalar_realization_coords.py b/lib/iris/tests/unit/fileformats/pp_load_rules/test__convert_scalar_realization_coords.py
index c00c4c1b5d..5d01eb5976 100644
--- a/lib/iris/tests/unit/fileformats/pp_load_rules/test__convert_scalar_realization_coords.py
+++ b/lib/iris/tests/unit/fileformats/pp_load_rules/test__convert_scalar_realization_coords.py
@@ -6,6 +6,7 @@
 :func:`iris.fileformats.pp_load_rules._convert_scalar_realization_coords`.
 
 """
+
 from iris.coords import DimCoord
 from iris.fileformats.pp_load_rules import _convert_scalar_realization_coords
 
diff --git a/lib/iris/tests/unit/fileformats/pp_load_rules/test__convert_time_coords.py b/lib/iris/tests/unit/fileformats/pp_load_rules/test__convert_time_coords.py
index a7656a8ec6..690f869a34 100644
--- a/lib/iris/tests/unit/fileformats/pp_load_rules/test__convert_time_coords.py
+++ b/lib/iris/tests/unit/fileformats/pp_load_rules/test__convert_time_coords.py
@@ -6,6 +6,7 @@
 :func:`iris.fileformats.pp_load_rules._convert_time_coords`.
 
 """
+
 from cf_units import CALENDAR_360_DAY, CALENDAR_STANDARD, Unit
 from cftime import datetime as nc_datetime
 import numpy as np
diff --git a/lib/iris/tests/unit/fileformats/pp_load_rules/test__convert_vertical_coords.py b/lib/iris/tests/unit/fileformats/pp_load_rules/test__convert_vertical_coords.py
index 0ba86a68b6..7f6270e9f3 100644
--- a/lib/iris/tests/unit/fileformats/pp_load_rules/test__convert_vertical_coords.py
+++ b/lib/iris/tests/unit/fileformats/pp_load_rules/test__convert_vertical_coords.py
@@ -6,6 +6,7 @@
 :func:`iris.fileformats.pp_load_rules._convert_vertical_coords`.
 
 """
+
 import numpy as np
 
 from iris.aux_factory import HybridHeightFactory, HybridPressureFactory
diff --git a/lib/iris/tests/unit/fileformats/pp_load_rules/test__dim_or_aux.py b/lib/iris/tests/unit/fileformats/pp_load_rules/test__dim_or_aux.py
index c532d4243a..496b82c6c8 100644
--- a/lib/iris/tests/unit/fileformats/pp_load_rules/test__dim_or_aux.py
+++ b/lib/iris/tests/unit/fileformats/pp_load_rules/test__dim_or_aux.py
@@ -3,6 +3,7 @@
 # This file is part of Iris and is released under the BSD license.
 # See LICENSE in the root of the repository for full licensing details.
 """Unit tests for :func:`iris.fileformats.pp_load_rules._dim_or_aux`."""
+
 import pytest
 
 from iris.coords import AuxCoord, DimCoord
diff --git a/lib/iris/tests/unit/fileformats/pp_load_rules/test__epoch_date_hours.py b/lib/iris/tests/unit/fileformats/pp_load_rules/test__epoch_date_hours.py
index 6db53bfcc8..826156dade 100644
--- a/lib/iris/tests/unit/fileformats/pp_load_rules/test__epoch_date_hours.py
+++ b/lib/iris/tests/unit/fileformats/pp_load_rules/test__epoch_date_hours.py
@@ -6,6 +6,7 @@
 :func:`iris.fileformats.pp_load_rules._epoch_date_hours`.
 
 """
+
 import cf_units
 from cf_units import Unit
 from cftime import datetime as nc_datetime
diff --git a/lib/iris/tests/unit/fileformats/pp_load_rules/test__model_level_number.py b/lib/iris/tests/unit/fileformats/pp_load_rules/test__model_level_number.py
index cff13616d6..c721e82754 100644
--- a/lib/iris/tests/unit/fileformats/pp_load_rules/test__model_level_number.py
+++ b/lib/iris/tests/unit/fileformats/pp_load_rules/test__model_level_number.py
@@ -3,6 +3,7 @@
 # This file is part of Iris and is released under the BSD license.
 # See LICENSE in the root of the repository for full licensing details.
 """Unit tests for :func:`iris.fileformats.pp_load_rules._model_level_number`."""
+
 from iris.fileformats.pp_load_rules import _model_level_number
 
 
diff --git a/lib/iris/tests/unit/fileformats/pp_load_rules/test__reduced_points_and_bounds.py b/lib/iris/tests/unit/fileformats/pp_load_rules/test__reduced_points_and_bounds.py
index 9e94273d63..72e59963e7 100644
--- a/lib/iris/tests/unit/fileformats/pp_load_rules/test__reduced_points_and_bounds.py
+++ b/lib/iris/tests/unit/fileformats/pp_load_rules/test__reduced_points_and_bounds.py
@@ -6,6 +6,7 @@
 :func:`iris.fileformats.pp_load_rules._reduce_points_and_bounds`.
 
 """
+
 import numpy as np
 
 from iris.fileformats.pp_load_rules import _reduce_points_and_bounds
diff --git a/lib/iris/tests/unit/fileformats/pp_load_rules/test__reshape_vector_args.py b/lib/iris/tests/unit/fileformats/pp_load_rules/test__reshape_vector_args.py
index 38cf0b9cb9..0bb8d55aae 100644
--- a/lib/iris/tests/unit/fileformats/pp_load_rules/test__reshape_vector_args.py
+++ b/lib/iris/tests/unit/fileformats/pp_load_rules/test__reshape_vector_args.py
@@ -6,6 +6,7 @@
 :func:`iris.fileformats.pp_load_rules._reshape_vector_args`.
 
 """
+
 import numpy as np
 import pytest
 
diff --git a/lib/iris/tests/unit/fileformats/pp_load_rules/test_convert.py b/lib/iris/tests/unit/fileformats/pp_load_rules/test_convert.py
index 08a6398f2d..d9e1e74e00 100644
--- a/lib/iris/tests/unit/fileformats/pp_load_rules/test_convert.py
+++ b/lib/iris/tests/unit/fileformats/pp_load_rules/test_convert.py
@@ -3,6 +3,7 @@
 # This file is part of Iris and is released under the BSD license.
 # See LICENSE in the root of the repository for full licensing details.
 """Unit tests for :func:`iris.fileformats.pp_load_rules.convert`."""
+
 from types import MethodType
 from unittest import mock
 
diff --git a/lib/iris/tests/unit/fileformats/rules/test_Loader.py b/lib/iris/tests/unit/fileformats/rules/test_Loader.py
index a11d2f96b6..08e0764a45 100644
--- a/lib/iris/tests/unit/fileformats/rules/test_Loader.py
+++ b/lib/iris/tests/unit/fileformats/rules/test_Loader.py
@@ -3,6 +3,7 @@
 # This file is part of Iris and is released under the BSD license.
 # See LICENSE in the root of the repository for full licensing details.
 """Unit tests for :class:`iris.fileformats.rules.Loader`."""
+
 from iris.fileformats.rules import Loader
 from iris.tests._shared_utils import assert_no_warnings_regexp
 
diff --git a/lib/iris/tests/unit/fileformats/rules/test__make_cube.py b/lib/iris/tests/unit/fileformats/rules/test__make_cube.py
index c7cd01193a..c14a5df705 100644
--- a/lib/iris/tests/unit/fileformats/rules/test__make_cube.py
+++ b/lib/iris/tests/unit/fileformats/rules/test__make_cube.py
@@ -3,6 +3,7 @@
 # This file is part of Iris and is released under the BSD license.
 # See LICENSE in the root of the repository for full licensing details.
 """Unit tests for :func:`iris.fileformats.rules._make_cube`."""
+
 from unittest import mock
 
 import numpy as np
diff --git a/lib/iris/tests/unit/fileformats/rules/test_rules.py b/lib/iris/tests/unit/fileformats/rules/test_rules.py
index 83dc202d71..df3c769a70 100644
--- a/lib/iris/tests/unit/fileformats/rules/test_rules.py
+++ b/lib/iris/tests/unit/fileformats/rules/test_rules.py
@@ -3,6 +3,7 @@
 # This file is part of Iris and is released under the BSD license.
 # See LICENSE in the root of the repository for full licensing details.
 """Test iris.fileformats.rules.py - metadata translation rules."""
+
 import types
 from unittest import mock
 
diff --git a/lib/iris/tests/unit/fileformats/structured_array_identification/test_ArrayStructure.py b/lib/iris/tests/unit/fileformats/structured_array_identification/test_ArrayStructure.py
index d8530db5e1..bf23b39a5c 100644
--- a/lib/iris/tests/unit/fileformats/structured_array_identification/test_ArrayStructure.py
+++ b/lib/iris/tests/unit/fileformats/structured_array_identification/test_ArrayStructure.py
@@ -6,6 +6,7 @@
 :mod:`iris.fileformats._structured_array_identification.ArrayStructure` class.
 
 """
+
 import numpy as np
 import pytest
 
diff --git a/lib/iris/tests/unit/lazy_data/test_map_complete_blocks.py b/lib/iris/tests/unit/lazy_data/test_map_complete_blocks.py
index c63f626fd9..be25ab6c09 100644
--- a/lib/iris/tests/unit/lazy_data/test_map_complete_blocks.py
+++ b/lib/iris/tests/unit/lazy_data/test_map_complete_blocks.py
@@ -47,7 +47,9 @@ def func(chunk):
     def test_non_lazy_input(self):
         # Check that a non-lazy input doesn't trip up the functionality.
         cube, cube_data = create_mock_cube(self.array)
-        result = map_complete_blocks(cube, self.func, dims=(1,), out_sizes=(4,), dtype=self.array.dtype)
+        result = map_complete_blocks(
+            cube, self.func, dims=(1,), out_sizes=(4,), dtype=self.array.dtype
+        )
         assert not is_lazy_data(result)
         assert_array_equal(result, self.func_result)
         # check correct data was accessed
@@ -57,7 +59,9 @@ def test_non_lazy_input(self):
     def test_lazy_input(self):
         lazy_array = da.asarray(self.array, chunks=((1, 1), (4,)))
         cube, cube_data = create_mock_cube(lazy_array)
-        result = map_complete_blocks(cube, self.func, dims=(1,), out_sizes=(4,), dtype=lazy_array.dtype)
+        result = map_complete_blocks(
+            cube, self.func, dims=(1,), out_sizes=(4,), dtype=lazy_array.dtype
+        )
         assert is_lazy_data(result)
         assert_array_equal(result.compute(), self.func_result)
         # check correct data was accessed
@@ -67,7 +71,8 @@ def test_lazy_input(self):
     def test_dask_array_input(self):
         lazy_array = da.asarray(self.array, chunks=((1, 1), (4,)))
         result = map_complete_blocks(
-            lazy_array, self.func, dims=(1,), out_sizes=(4,), dtype=lazy_array.dtype)
+            lazy_array, self.func, dims=(1,), out_sizes=(4,), dtype=lazy_array.dtype
+        )
         assert is_lazy_data(result)
         assert_array_equal(result.compute(), self.func_result)
 
@@ -100,7 +105,9 @@ def func(chunk):
     def test_rechunk(self):
         lazy_array = da.asarray(self.array, chunks=((1, 1), (2, 2)))
         cube, _ = create_mock_cube(lazy_array)
-        result = map_complete_blocks(cube, self.func, dims=(1,), out_sizes=(4,), dtype=lazy_array.dtype)
+        result = map_complete_blocks(
+            cube, self.func, dims=(1,), out_sizes=(4,), dtype=lazy_array.dtype
+        )
         assert is_lazy_data(result)
         assert_array_equal(result.compute(), self.func_result)
 
@@ -112,7 +119,9 @@ def func(_):
             return np.arange(2).reshape(1, 2)
 
         func_result = [[0, 1], [0, 1]]
-        result = map_complete_blocks(cube, func, dims=(1,), out_sizes=(2,), dtype=lazy_array.dtype)
+        result = map_complete_blocks(
+            cube, func, dims=(1,), out_sizes=(2,), dtype=lazy_array.dtype
+        )
         assert is_lazy_data(result)
         assert_array_equal(result.compute(), func_result)
 
@@ -120,6 +129,8 @@ def test_multidimensional_input(self):
         array = np.arange(2 * 3 * 4).reshape(2, 3, 4)
         lazy_array = da.asarray(array, chunks=((1, 1), (1, 2), (4,)))
         cube, _ = create_mock_cube(lazy_array)
-        result = map_complete_blocks(cube, self.func, dims=(1, 2), out_sizes=(3, 4), dtype=lazy_array.dtype)
+        result = map_complete_blocks(
+            cube, self.func, dims=(1, 2), out_sizes=(3, 4), dtype=lazy_array.dtype
+        )
         assert is_lazy_data(result)
         assert_array_equal(result.compute(), array + 1)
diff --git a/lib/iris/tests/unit/plot/test__get_plot_defn_custom_coords_picked.py b/lib/iris/tests/unit/plot/test__get_plot_defn_custom_coords_picked.py
index 80f01be708..defae2ca86 100644
--- a/lib/iris/tests/unit/plot/test__get_plot_defn_custom_coords_picked.py
+++ b/lib/iris/tests/unit/plot/test__get_plot_defn_custom_coords_picked.py
@@ -5,6 +5,7 @@
 """Unit tests for the `iris.plot._get_plot_defn_custom_coords_picked`
 function.
 """
+
 import pytest
 
 from iris.coords import BOUND_MODE, POINT_MODE
diff --git a/lib/iris/tests/unit/plot/test__get_plot_objects.py b/lib/iris/tests/unit/plot/test__get_plot_objects.py
index 20eea759af..a0ae48141a 100644
--- a/lib/iris/tests/unit/plot/test__get_plot_objects.py
+++ b/lib/iris/tests/unit/plot/test__get_plot_objects.py
@@ -3,6 +3,7 @@
 # This file is part of Iris and is released under the BSD license.
 # See LICENSE in the root of the repository for full licensing details.
 """Unit tests for the `iris.plot._get_plot_objects` function."""
+
 import pytest
 
 import iris.cube
diff --git a/lib/iris/tests/unit/plot/test_outline.py b/lib/iris/tests/unit/plot/test_outline.py
index 615febfed2..2c84a6c718 100644
--- a/lib/iris/tests/unit/plot/test_outline.py
+++ b/lib/iris/tests/unit/plot/test_outline.py
@@ -3,6 +3,7 @@
 # This file is part of Iris and is released under the BSD license.
 # See LICENSE in the root of the repository for full licensing details.
 """Unit tests for the `iris.plot.outline` function."""
+
 import numpy as np
 import pytest
 
diff --git a/lib/iris/tests/unit/plot/test_points.py b/lib/iris/tests/unit/plot/test_points.py
index 41babd53d6..e8778ed30e 100644
--- a/lib/iris/tests/unit/plot/test_points.py
+++ b/lib/iris/tests/unit/plot/test_points.py
@@ -3,6 +3,7 @@
 # This file is part of Iris and is released under the BSD license.
 # See LICENSE in the root of the repository for full licensing details.
 """Unit tests for the `iris.plot.points` function."""
+
 import numpy as np
 import pytest
 
diff --git a/lib/iris/tests/unit/util/test__slice_data_with_keys.py b/lib/iris/tests/unit/util/test__slice_data_with_keys.py
index e6b4067cb5..fd692e2076 100644
--- a/lib/iris/tests/unit/util/test__slice_data_with_keys.py
+++ b/lib/iris/tests/unit/util/test__slice_data_with_keys.py
@@ -11,6 +11,7 @@
 in combination.
 
 """
+
 import numpy as np
 import pytest
 
diff --git a/lib/iris/tests/unit/util/test_file_is_newer_than.py b/lib/iris/tests/unit/util/test_file_is_newer_than.py
index 3e5e997835..bba3f1fe37 100644
--- a/lib/iris/tests/unit/util/test_file_is_newer_than.py
+++ b/lib/iris/tests/unit/util/test_file_is_newer_than.py
@@ -3,6 +3,7 @@
 # This file is part of Iris and is released under the BSD license.
 # See LICENSE in the root of the repository for full licensing details.
 """Test function :func:`iris.util.test_file_is_newer`."""
+
 import os
 import os.path
 
diff --git a/lib/iris/tests/unit/util/test_reverse.py b/lib/iris/tests/unit/util/test_reverse.py
index 10d80c8a2e..77d6df0251 100644
--- a/lib/iris/tests/unit/util/test_reverse.py
+++ b/lib/iris/tests/unit/util/test_reverse.py
@@ -3,6 +3,7 @@
 # This file is part of Iris and is released under the BSD license.
 # See LICENSE in the root of the repository for full licensing details.
 """Test function :func:`iris.util.reverse`."""
+
 import numpy as np
 import pytest
 
diff --git a/lib/iris/tests/unit/util/test_rolling_window.py b/lib/iris/tests/unit/util/test_rolling_window.py
index 90a6983cff..c2e5bdbb6c 100644
--- a/lib/iris/tests/unit/util/test_rolling_window.py
+++ b/lib/iris/tests/unit/util/test_rolling_window.py
@@ -3,6 +3,7 @@
 # This file is part of Iris and is released under the BSD license.
 # See LICENSE in the root of the repository for full licensing details.
 """Test function :func:`iris.util.rolling_window`."""
+
 import dask.array as da
 import numpy as np
 import numpy.ma as ma
diff --git a/lib/iris/tests/unit/util/test_squeeze.py b/lib/iris/tests/unit/util/test_squeeze.py
index e4cc4dc9a7..c1a63a64b6 100644
--- a/lib/iris/tests/unit/util/test_squeeze.py
+++ b/lib/iris/tests/unit/util/test_squeeze.py
@@ -3,6 +3,7 @@
 # This file is part of Iris and is released under the BSD license.
 # See LICENSE in the root of the repository for full licensing details.
 """Test function :func:`iris.util.squeeze`."""
+
 import pytest
 
 import iris
diff --git a/lib/iris/tests/unit/util/test_unify_time_units.py b/lib/iris/tests/unit/util/test_unify_time_units.py
index 9b2a6dd170..ceccc459ce 100644
--- a/lib/iris/tests/unit/util/test_unify_time_units.py
+++ b/lib/iris/tests/unit/util/test_unify_time_units.py
@@ -3,6 +3,7 @@
 # This file is part of Iris and is released under the BSD license.
 # See LICENSE in the root of the repository for full licensing details.
 """Test function :func:`iris.util.array_equal`."""
+
 import copy
 
 import cf_units