diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 806fa0d0800..dec9a0ac4a0 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -31,7 +31,7 @@ jobs:
         apt:
           - libopenjp2-7
       envs: |
-        - linux: py311
+        - linux: py312
     secrets:
       CODECOV_TOKEN: ${{ secrets.CODECOV_TOKEN }}
 
@@ -47,8 +47,9 @@ jobs:
         brew:
           - openjpeg
       envs: |
-        - windows: py310
-        - macos: py39
+        - windows: py311
+        - macos: py310
+        - linux: py39
         - linux: py39-oldestdeps
     secrets:
       CODECOV_TOKEN: ${{ secrets.CODECOV_TOKEN }}
@@ -178,9 +179,9 @@ jobs:
       test_command: 'pytest -p no:warnings --doctest-rst -m "not mpl_image_compare" --pyargs sunpy'
       submodules: false
       targets: |
-        - cp3{9,10,11}-manylinux*_x86_64
-        - cp3{9,10,11}-macosx_x86_64
-        - cp3{9,10,11}-macosx_arm64
+        - cp3{9,10,11,12}-manylinux*_x86_64
+        - cp3{9,10,11,12}-macosx_x86_64
+        - cp3{9,10,11,12}-macosx_arm64
     secrets:
       pypi_token: ${{ secrets.pypi_token }}
 
diff --git a/changelog/7351.feature.rst b/changelog/7351.feature.rst
new file mode 100644
index 00000000000..d35054f41a0
--- /dev/null
+++ b/changelog/7351.feature.rst
@@ -0,0 +1 @@
+Added testing and explicit support for Python 3.12.
diff --git a/setup.cfg b/setup.cfg
index b2b07e73ca7..0c4643acb97 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -30,6 +30,7 @@ classifiers =
   Programming Language :: Python :: 3.9
   Programming Language :: Python :: 3.10
   Programming Language :: Python :: 3.11
+  Programming Language :: Python :: 3.12
   Topic :: Scientific/Engineering :: Physics
 
 [options]
@@ -60,7 +61,7 @@ image =
   scipy>=1.7.0,!=1.10.0
 jpeg2000 =
   glymur>=0.9.1,!=0.9.5
-  lxml>=4.8.0
+  lxml>=4.8.0,!=5.0.0
 map =
   matplotlib>=3.5.0
   mpl-animators>=1.0.0
@@ -236,6 +237,8 @@ filterwarnings =
     ignore:.*module is deprecated, as it was designed for internal use
     # This is raised when the VSO redirects and we do not want this to stop the CI
     ignore::sunpy.util.exceptions.SunpyConnectionWarning
+    # Can be removed when https://github.com/dateutil/dateutil/issues/1314 is resolved
+    ignore:datetime.datetime.utcfromtimestamp():DeprecationWarning
 
 [pycodestyle]
 max_line_length = 110
@@ -273,7 +276,6 @@ omit =
   sunpy/cython_version*
   sunpy/*setup*
   sunpy/extern/*
-  sunpy/*/tests/*
   sunpy/version*
   sunpy/__init__*
   sunpy/data/sample.py
@@ -283,7 +285,6 @@ omit =
   */sunpy/cython_version*
   */sunpy/*setup*
   */sunpy/extern/*
-  */sunpy/*/tests/*
   */sunpy/version*
   */sunpy/__init__*
   */sunpy/data/sample.py
diff --git a/sunpy/map/header_helper.py b/sunpy/map/header_helper.py
index f0c19cd908f..6456a612a3f 100644
--- a/sunpy/map/header_helper.py
+++ b/sunpy/map/header_helper.py
@@ -408,7 +408,33 @@ def make_heliographic_header(date, observer_coordinate, shape, *, frame, project
     >>> observer = get_earth(date)
     >>> header = make_heliographic_header(date, observer, [90, 180], frame='carrington')
     >>> header
-    MetaDict([('wcsaxes', 2), ('crpix1', 90.5), ('crpix2', 45.5), ('cdelt1', 2.0), ('cdelt2', 2.0), ('cunit1', 'deg'), ('cunit2', 'deg'), ('ctype1', 'CRLN-CAR'), ('ctype2', 'CRLT-CAR'), ('crval1', 0.0), ('crval2', 0.0), ('lonpole', 0.0), ('latpole', 90.0), ('mjdref', 0.0), ('date-obs', '2020-01-01T12:00:00.000'), ('rsun_ref', 695700000.0), ('dsun_obs', 147096975776.97), ('hgln_obs', 0.0), ('hglt_obs', -3.0011725838606), ('naxis', 2), ('naxis1', 180), ('naxis2', 90), ('pc1_1', 1.0), ('pc1_2', -0.0), ('pc2_1', 0.0), ('pc2_2', 1.0), ('rsun_obs', 975.5398432033492)])
+    MetaDict([('wcsaxes': '2')
+    ('crpix1': '90.5')
+    ('crpix2': '45.5')
+    ('cdelt1': '2.0')
+    ('cdelt2': '2.0')
+    ('cunit1': 'deg')
+    ('cunit2': 'deg')
+    ('ctype1': 'CRLN-CAR')
+    ('ctype2': 'CRLT-CAR')
+    ('crval1': '0.0')
+    ('crval2': '0.0')
+    ('lonpole': '0.0')
+    ('latpole': '90.0')
+    ('mjdref': '0.0')
+    ('date-obs': '2020-01-01T12:00:00.000')
+    ('rsun_ref': '695700000.0')
+    ('dsun_obs': '147096975776.97')
+    ('hgln_obs': '0.0')
+    ('hglt_obs': '-3.0011725838606')
+    ('naxis': '2')
+    ('naxis1': '180')
+    ('naxis2': '90')
+    ('pc1_1': '1.0')
+    ('pc1_2': '-0.0')
+    ('pc2_1': '0.0')
+    ('pc2_2': '1.0')
+    ('rsun_obs': '975.53984320334...
 
     .. minigallery:: sunpy.map.make_heliographic_header
     """
diff --git a/sunpy/net/dataretriever/sources/tests/test_noaa.py b/sunpy/net/dataretriever/sources/tests/test_noaa.py
index 60f43d951b9..49a36b55ab4 100644
--- a/sunpy/net/dataretriever/sources/tests/test_noaa.py
+++ b/sunpy/net/dataretriever/sources/tests/test_noaa.py
@@ -129,8 +129,10 @@ def test_fetch(mock_wait, mock_search, mock_enqueue, tmp_path, indices_client):
     # Downloader.enqueue_file method with the correct arguments. Everything
     # that happens after this point should either be tested in the
     # GenericClient tests or in parfive itself.
-    assert mock_enqueue.called_once_with(("https://services.swpc.noaa.gov/json/solar-cycle/observed-solar-cycle-indices.json",
-                                          path / "observed-solar-cycle-indices.json"))
+    mock_enqueue.assert_called_once_with(
+        Time("2012-10-04 00:00:00.000", "2012-10-06 00:00:00.000"),
+        Instrument("noaa-indices")
+    )
 
 
 @mock.patch('sunpy.net.dataretriever.sources.noaa.NOAAIndicesClient.search',
@@ -151,8 +153,10 @@ def test_fido(mock_wait, mock_search, mock_enqueue, tmp_path, indices_client):
     # Downloader.enqueue_file method with the correct arguments. Everything
     # that happens after this point should either be tested in the
     # GenericClient tests or in parfive itself.
-    assert mock_enqueue.called_once_with(("https://services.swpc.noaa.gov/json/solar-cycle/observed-solar-cycle-indices.json",
-                                          path / "observed-solar-cycle-indices.json"))
+    mock_enqueue.assert_called_once_with(
+        Time('2012-10-04 00:00:00.000', '2012-10-06 00:00:00.000'),
+        Instrument("noaa-indices")
+    )
 
 
 @no_vso
diff --git a/sunpy/net/jsoc/tests/test_jsoc.py b/sunpy/net/jsoc/tests/test_jsoc.py
index 6070cb4812c..0fb98a94d6d 100644
--- a/sunpy/net/jsoc/tests/test_jsoc.py
+++ b/sunpy/net/jsoc/tests/test_jsoc.py
@@ -321,7 +321,7 @@ def test_row_and_warning(mocker, client, jsoc_response_double):
     request_data = mocker.patch("sunpy.net.jsoc.jsoc.JSOCClient.request_data")
     with pytest.warns(SunpyUserWarning):
         client.fetch(jsoc_response_double[0], sleep=0)
-    assert request_data.called_once_with(jsoc_response_double[0].as_table())
+    request_data.assert_called_once_with(jsoc_response_double[0].as_table())
 
 
 @pytest.mark.remote_data
diff --git a/sunpy/net/tests/strategies.py b/sunpy/net/tests/strategies.py
index 39f54fc219f..ac02ebb23d9 100644
--- a/sunpy/net/tests/strategies.py
+++ b/sunpy/net/tests/strategies.py
@@ -15,14 +15,14 @@
 from sunpy.net import attrs as a
 from sunpy.time import TimeRange, parse_time
 
-TimesLeapsecond = sampled_from((Time('2015-06-30T23:59:60'),
+TIME_LEAP_SECONDS = sampled_from((Time('2015-06-30T23:59:60'),
                                 Time('2012-06-30T23:59:60')))
 
 
 @st.composite
 def Times(draw, max_value, min_value):
     time = one_of(datetimes(max_value=max_value, min_value=min_value),
-                  TimesLeapsecond)
+                  TIME_LEAP_SECONDS)
 
     time = Time(draw(time))
 
@@ -74,7 +74,7 @@ def online_instruments():
 
 @st.composite
 def time_attr(draw, time=Times(
-              max_value=datetime.datetime(datetime.datetime.utcnow().year, 1, 1, 0, 0),
+              max_value=datetime.datetime(datetime.datetime.now(datetime.timezone.utc).year, 1, 1, 0, 0),
               min_value=datetime.datetime(1981, 1, 1, 0, 0)),
               delta=TimeDelta()):
     """
@@ -90,7 +90,7 @@ def time_attr(draw, time=Times(
 
 @st.composite
 def goes_time(draw, time=Times(
-              max_value=datetime.datetime(datetime.datetime.utcnow().year, 1, 1, 0, 0),
+              max_value=datetime.datetime(datetime.datetime.now(datetime.timezone.utc).year, 1, 1, 0, 0),
               min_value=datetime.datetime(1981, 1, 1, 0, 0)),
               delta=TimeDelta()):
     """
@@ -116,7 +116,7 @@ def goes_time(draw, time=Times(
 
 @st.composite
 def srs_time(draw, time=Times(
-             max_value=datetime.datetime.now(),
+             max_value=datetime.datetime.now(datetime.timezone.utc),
              min_value=datetime.datetime(1996, 1, 1)),
              delta=TimeDelta()):
     t1 = draw(time)
diff --git a/sunpy/time/tests/test_time.py b/sunpy/time/tests/test_time.py
index b5156d44ad7..4d0251deb51 100644
--- a/sunpy/time/tests/test_time.py
+++ b/sunpy/time/tests/test_time.py
@@ -1,4 +1,4 @@
-from datetime import date, datetime
+from datetime import date, datetime, timezone
 
 import numpy as np
 import pandas
@@ -352,7 +352,7 @@ def test_parse_time_list_3():
 
 
 def test_is_time():
-    assert time.is_time(datetime.utcnow()) is True
+    time.is_time(datetime.now(timezone.utc)) is True
     assert time.is_time('2017-02-14 08:08:12.999') is True
     assert time.is_time(Time.now()) is True
 
diff --git a/sunpy/timeseries/metadata.py b/sunpy/timeseries/metadata.py
index 947bd38a2dc..c54a2f6008d 100644
--- a/sunpy/timeseries/metadata.py
+++ b/sunpy/timeseries/metadata.py
@@ -72,7 +72,7 @@ class TimeSeriesMetaData:
     >>> md.find(parse_time('2012-06-01T21:08:12')).values()
     ['eve_val', 'goes_val']
     >>> md.find(parse_time('2012-06-01T21:08:12')).metas
-    [MetaDict([('goes_key', 'goes_val')]), MetaDict([('eve_key', 'eve_val')])]
+    [MetaDict([('goes_key': 'goes_val')]), MetaDict([('eve_key': 'eve_val')])]
     >>> md.find(parse_time('2012-06-01T21:08:12'), 'GOES')
     |-------------------------------------------------------------------------------------------------|
     |TimeRange                  | Columns         | Meta                                              |
diff --git a/sunpy/util/metadata.py b/sunpy/util/metadata.py
index 213977d5486..74b19ae769a 100644
--- a/sunpy/util/metadata.py
+++ b/sunpy/util/metadata.py
@@ -68,7 +68,10 @@ def __init__(self, *args, save_original=True):
             self._original_meta = MetaDict(*args, save_original=False)
 
     def __str__(self):
-        return '\n'.join([f'{key}: {item}' for key, item in self.items()])
+        return '\n'.join([f"('{key}': '{item}')" for key, item in self.items()])
+
+    def __repr__(self):
+        return f"{self.__class__.__name__}([{self}])"
 
     # Deliberately a property to prevent external modification
     @property
diff --git a/tox.ini b/tox.ini
index 95fcc997256..31c76210f23 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,7 +1,7 @@
 [tox]
 min_version = 4.0
 envlist =
-    py{39,310,311}{,-oldestdeps,-devdeps,-online,-figure,-conda}
+    py{39,310,311,312}{,-oldestdeps,-devdeps,-online,-figure,-conda}
     build_docs{,-gallery}
     codestyle
     base_deps