Tests showing behaviour with pytest importlib mode.

.github/workflows/ci.yaml

@@ -46,3 +46,35 @@ jobs:
 
       - name: Run tests
         run: tox -e py
+
+  import-mode-importlib:
+    name: import-mode=importlib
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@master
+
+      - name: Set up Python
+        uses: actions/setup-python@v2
+
+      - name: Install tox
+        run: pip install tox
+
+      - name: Run tests
+        run: tox -e import-mode-importlib
+
+  import-mode-prepend:
+    name: import-mode=prepend
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@master
+
+      - name: Set up Python
+        uses: actions/setup-python@v2
+
+      - name: Install tox
+        run: pip install tox
+
+      - name: Run tests
+        run: tox -e import-mode-prepend

tests/test_importlib.py

@@ -0,0 +1,17 @@
+from datetime import datetime as from_datetime
+import datetime as toplevel_datetime
+
+from freezegun import freeze_time
+
+
+def test_from_datetime():
+    # Importing the datetime class doesn't work when pytest is using import-mode=importlib.
+    # This is supposed to become the default, according to the documentation: https://docs.pytest.org/en/latest/changelog.html?highlight=importlib#pytest-6-0-0rc1-2020-07-08
+    with freeze_time("2019-01-01"):
+        assert from_datetime.utcnow().year == 2019
+
+
+def test_top_level_datetime():
+    # freezegun works as expected when we're importing the datetime module
+    with freeze_time("2019-01-01"):
+        assert toplevel_datetime.datetime.utcnow().year == 2019

tox.ini

@@ -4,12 +4,20 @@
 # and then run "tox" from this directory.
 
 [tox]
-envlist = py36, py37, py38, py39, pypy3, mypy
+envlist = py36, py37, py38, py39, pypy3, mypy, import-mode-importlib, import-mode-prepend
 
 [testenv]
 commands = pytest --cov {posargs}
 deps = -rrequirements.txt
 
+[testenv:import-mode-importlib]
+commands = pytest --import-mode=importlib tests/test_importlib.py
+deps = -rrequirements.txt
+
+[testenv:import-mode-prepend]
+commands = pytest --import-mode=prepend tests/test_importlib.py
+deps = -rrequirements.txt
+
 [testenv:mypy]
 deps =
     mypy