diff --git a/test_autofit/aggregator/summary_files/test_aggregate_fits.py b/test_autofit/aggregator/summary_files/test_aggregate_fits.py
index aa11d584c..b3fccf8b0 100644
--- a/test_autofit/aggregator/summary_files/test_aggregate_fits.py
+++ b/test_autofit/aggregator/summary_files/test_aggregate_fits.py
@@ -1,3 +1,4 @@
+import importlib.util
 from enum import Enum
 import pytest
 
@@ -5,6 +6,17 @@
 from pathlib import Path
 
 
+# `astropy` ships via the `[optional]` extras. Envs installed without them
+# must skip rather than fail with `No module named 'astropy'`.
+requires_astropy = pytest.mark.skipif(
+    importlib.util.find_spec("astropy") is None,
+    reason="requires astropy (installed via the [optional] extras)",
+)
+
+
+pytestmark = requires_astropy
+
+
 class FITSFit(Enum):
     """
     The HDUs that can be extracted from the fit.fits file.
diff --git a/test_autofit/aggregator/test_child_analysis.py b/test_autofit/aggregator/test_child_analysis.py
index e9e2a68b1..123963150 100644
--- a/test_autofit/aggregator/test_child_analysis.py
+++ b/test_autofit/aggregator/test_child_analysis.py
@@ -1,3 +1,4 @@
+import importlib.util
 from pathlib import Path
 
 import pytest
@@ -7,6 +8,14 @@
 import autofit as af
 
 
+# `astropy` ships via the `[optional]` extras. Envs installed without them
+# must skip rather than fail with `No module named 'astropy'`.
+requires_astropy = pytest.mark.skipif(
+    importlib.util.find_spec("astropy") is None,
+    reason="requires astropy (installed via the [optional] extras)",
+)
+
+
 @pytest.fixture(name="directory")
 def make_directory():
     return Path(__file__).parent
@@ -50,12 +59,14 @@ def make_aggregator(session, directory):
     return aggregator
 
 
+@requires_astropy
 def test_database_aggregator(aggregator):
     assert list(aggregator.child_values("example")) == [
         ["hello world", "hello world"],
     ]
 
 
+@requires_astropy
 def test_child_values(aggregator):
     fit, *_ = list(aggregator)
     assert fit.child_values("example") == ["hello world", "hello world"]
diff --git a/test_autofit/aggregator/test_reference.py b/test_autofit/aggregator/test_reference.py
index 118a75729..f14841d19 100644
--- a/test_autofit/aggregator/test_reference.py
+++ b/test_autofit/aggregator/test_reference.py
@@ -1,3 +1,4 @@
+import importlib.util
 import os
 
 import pytest
@@ -9,6 +10,14 @@
 from autofit.database.aggregator.info import Info
 
 
+# `astropy` ships via the `[optional]` extras. Envs installed without them
+# must skip rather than fail with `No module named 'astropy'`.
+requires_astropy = pytest.mark.skipif(
+    importlib.util.find_spec("astropy") is None,
+    reason="requires astropy (installed via the [optional] extras)",
+)
+
+
 @pytest.fixture(name="directory")
 def make_directory():
     return Path(__file__).parent
@@ -56,6 +65,7 @@ def database_aggregator(
     return aggregator
 
 
+@requires_astropy
 def test_database(database_aggregator):
     fit = list(database_aggregator)[0]
     model = fit.model
@@ -67,20 +77,24 @@ def make_info(database_aggregator):
     return Info(database_aggregator.session)
 
 
+@requires_astropy
 def test_query_fits(info):
     fits = info.fits
     assert len(info.fits) == 3
     assert fits[0].total_parameters == 4
 
 
+@requires_astropy
 def test_headers_and_rows(info):
     assert len(info.headers) == len(info.rows[0])
 
 
+@requires_astropy
 def test_info_path(info, output_directory):
     assert info.path == output_directory / "database.info"
 
 
+@requires_astropy
 def test_database_info(
     database_aggregator,
     output_directory,
diff --git a/test_autofit/aggregator/test_scrape.py b/test_autofit/aggregator/test_scrape.py
index 70cf35b56..9cdaf2e4f 100644
--- a/test_autofit/aggregator/test_scrape.py
+++ b/test_autofit/aggregator/test_scrape.py
@@ -1,9 +1,19 @@
+import importlib.util
+
 import pytest
 
 from autofit import SearchOutput
 from autofit.database.aggregator.scrape import _add_files
 
 
+# `astropy` ships via the `[optional]` extras. Envs installed without them
+# must skip rather than fail with `No module named 'astropy'`.
+requires_astropy = pytest.mark.skipif(
+    importlib.util.find_spec("astropy") is None,
+    reason="requires astropy (installed via the [optional] extras)",
+)
+
+
 class MockFit:
     def __init__(self):
         self.jsons = {}
@@ -36,6 +46,7 @@ def make_fit(directory):
     return fit
 
 
+@requires_astropy
 def test_add_files(fit):
     assert fit.jsons["model"] == {
         "class_path": "autofit.example.model.Gaussian",
@@ -63,6 +74,7 @@ def test_add_files(fit):
     }
 
 
+@requires_astropy
 def test_add_recursive(fit):
     assert fit.jsons["directory.example"] == {
         "hello": "world",
diff --git a/test_autofit/database/test_file_types.py b/test_autofit/database/test_file_types.py
index 8500a79cf..59bc8e161 100644
--- a/test_autofit/database/test_file_types.py
+++ b/test_autofit/database/test_file_types.py
@@ -3,6 +3,14 @@
 
 from autofit.database import JSON
 from autofit import database as db
+
+# `astropy` ships via the `[optional]` extras; skip the module there
+# rather than fail collection with `No module named 'astropy'`.
+pytest.importorskip(
+    "astropy",
+    reason="requires astropy (installed via the [optional] extras)",
+)
+
 from astropy.io import fits
 
 
diff --git a/test_autofit/non_linear/paths/test_save_and_load.py b/test_autofit/non_linear/paths/test_save_and_load.py
index 3e5aa3e7f..be4e66745 100644
--- a/test_autofit/non_linear/paths/test_save_and_load.py
+++ b/test_autofit/non_linear/paths/test_save_and_load.py
@@ -1,9 +1,17 @@
 import numpy as np
 import pytest
-from astropy.io import fits
 
 import autofit as af
 
+# `astropy` ships via the `[optional]` extras; skip the module there
+# rather than fail collection with `No module named 'astropy'`.
+pytest.importorskip(
+    "astropy",
+    reason="requires astropy (installed via the [optional] extras)",
+)
+
+from astropy.io import fits
+
 
 @pytest.fixture(name="dictionary")
 def make_dictionary():
diff --git a/test_autofit/non_linear/search/nest/test_nautilus.py b/test_autofit/non_linear/search/nest/test_nautilus.py
index ca217876b..87e621157 100644
--- a/test_autofit/non_linear/search/nest/test_nautilus.py
+++ b/test_autofit/non_linear/search/nest/test_nautilus.py
@@ -1,3 +1,5 @@
+import importlib.util
+
 import numpy as np
 import pytest
 
@@ -5,6 +7,15 @@
 
 pytestmark = pytest.mark.filterwarnings("ignore::FutureWarning")
 
+# The regression test below runs a real `search.fit`, which imports the
+# `nautilus` sampler; it ships via the `[optional]` extras. Envs installed
+# without those extras must skip rather than fail with
+# `No module named 'nautilus'` — the other tests here only read config.
+requires_nautilus = pytest.mark.skipif(
+    importlib.util.find_spec("nautilus") is None,
+    reason="requires nautilus-sampler (installed via the [optional] extras)",
+)
+
 
 def test__explicit_params():
     search = af.Nautilus(
@@ -54,6 +65,7 @@ def test__test_mode():
     assert search.n_like_max == 1
 
 
+@requires_nautilus
 def test__single_core_builds_no_pool(monkeypatch):
     """
     number_of_cores=1 must not construct a multiprocessing pool: nautilus