5 files changed, 83 insertions, 56 deletions

diff --git a/tests/README.md b/tests/README.md
new file mode 100644
index 000000000..a0f110f08
--- /dev/null
+++ b/tests/README.md
@@ -0,0 +1,20 @@
+# Repo Tests
+
+There is a mixture of [pytest] & [Python unittest] in here.  We adopted [pytest]
+later on but didn't migrate existing tests (since they still work).  New tests
+should be written using [pytest] only.
+
+## File layout
+
+*   `test_xxx.py`: Unittests for the `xxx` module in the main repo codebase.
+    Modules that are in subdirs normalize the `/` into `_`.
+    For example, [test_error.py](./test_error.py) is for the
+    [error.py](../error.py) module, and
+    [test_subcmds_forall.py](./test_subcmds_forall.py) is for the
+    [subcmds/forall.py](../subcmds/forall.py) module.
+*   [conftest.py](./conftest.py): Custom pytest fixtures for sharing.
+*   [utils_for_test.py](./utils_for_test.py): Helpers for sharing in tests.
+
+
+[pytest]: https://pytest.org/
+[Python unittest]: https://docs.python.org/3/library/unittest.html#unittest.TestCase
diff --git a/tests/test_project.py b/tests/test_project.py
index de26e91a1..e0a6dec07 100644
--- a/tests/test_project.py
+++ b/tests/test_project.py
@@ -21,33 +21,15 @@ import subprocess
 import tempfile
 import unittest
 
+import utils_for_test
+
 import error
-import git_command
 import git_config
 import manifest_xml
 import platform_utils
 import project
 
 
-@contextlib.contextmanager
-def TempGitTree():
-    """Create a new empty git checkout for testing."""
-    with tempfile.TemporaryDirectory(prefix="repo-tests") as tempdir:
-        # Tests need to assume, that main is default branch at init,
-        # which is not supported in config until 2.28.
-        cmd = ["git", "init"]
-        if git_command.git_require((2, 28, 0)):
-            cmd += ["--initial-branch=main"]
-        else:
-            # Use template dir for init.
-            templatedir = tempfile.mkdtemp(prefix=".test-template")
-            with open(os.path.join(templatedir, "HEAD"), "w") as fp:
-                fp.write("ref: refs/heads/main\n")
-            cmd += ["--template", templatedir]
-        subprocess.check_call(cmd, cwd=tempdir)
-        yield tempdir
-
-
 class FakeProject:
     """A fake for Project for basic functionality."""
 
@@ -69,7 +51,7 @@ class ReviewableBranchTests(unittest.TestCase):
 
     def test_smoke(self):
         """A quick run through everything."""
-        with TempGitTree() as tempdir:
+        with utils_for_test.TempGitTree() as tempdir:
             fakeproj = FakeProject(tempdir)
 
             # Generate some commits.
@@ -467,7 +449,7 @@ class ManifestPropertiesFetchedCorrectly(unittest.TestCase):
     def test_manifest_config_properties(self):
         """Test we are fetching the manifest config properties correctly."""
 
-        with TempGitTree() as tempdir:
+        with utils_for_test.TempGitTree() as tempdir:
             fakeproj = self.setUpManifest(tempdir)
 
             # Set property using the expected Set method, then ensure
diff --git a/tests/test_subcmds_forall.py b/tests/test_subcmds_forall.py
index 84744f893..e50b28d8a 100644
--- a/tests/test_subcmds_forall.py
+++ b/tests/test_subcmds_forall.py
@@ -17,12 +17,12 @@
 from io import StringIO
 import os
 from shutil import rmtree
-import subprocess
 import tempfile
 import unittest
 from unittest import mock
 
-import git_command
+import utils_for_test
+
 import manifest_xml
 import project
 import subcmds
@@ -50,24 +50,6 @@ class AllCommands(unittest.TestCase):
         """Common teardown."""
         rmtree(self.tempdir, ignore_errors=True)
 
-    def initTempGitTree(self, git_dir):
-        """Create a new empty git checkout for testing."""
-
-        # Tests need to assume, that main is default branch at init,
-        # which is not supported in config until 2.28.
-        cmd = ["git", "init", "-q"]
-        if git_command.git_require((2, 28, 0)):
-            cmd += ["--initial-branch=main"]
-        else:
-            # Use template dir for init
-            templatedir = os.path.join(self.tempdirobj.name, ".test-template")
-            os.makedirs(templatedir)
-            with open(os.path.join(templatedir, "HEAD"), "w") as fp:
-                fp.write("ref: refs/heads/main\n")
-            cmd += ["--template", templatedir]
-        cmd += [git_dir]
-        subprocess.check_call(cmd)
-
     def getXmlManifestWith8Projects(self):
         """Create and return a setup of 8 projects with enough dummy
         files and setup to execute forall."""
@@ -114,7 +96,7 @@ class AllCommands(unittest.TestCase):
                 )
             )
             git_path = os.path.join(self.tempdir, "tests/path" + str(x))
-            self.initTempGitTree(git_path)
+            utils_for_test.init_git_tree(git_path)
 
         return manifest_xml.XmlManifest(self.repodir, self.manifest_file)
 
diff --git a/tests/test_wrapper.py b/tests/test_wrapper.py
index 77ceda8f7..a38705675 100644
--- a/tests/test_wrapper.py
+++ b/tests/test_wrapper.py
@@ -23,7 +23,8 @@ import tempfile
 import unittest
 from unittest import mock
 
-import git_command
+import utils_for_test
+
 import main
 import wrapper
 
@@ -408,18 +409,7 @@ class GitCheckoutTestCase(RepoWrapperTestCase):
         remote = os.path.join(cls.GIT_DIR, "remote")
         os.mkdir(remote)
 
-        # Tests need to assume, that main is default branch at init,
-        # which is not supported in config until 2.28.
-        if git_command.git_require((2, 28, 0)):
-            initstr = "--initial-branch=main"
-        else:
-            # Use template dir for init.
-            templatedir = tempfile.mkdtemp(prefix=".test-template")
-            with open(os.path.join(templatedir, "HEAD"), "w") as fp:
-                fp.write("ref: refs/heads/main\n")
-            initstr = "--template=" + templatedir
-
-        run_git("init", initstr, cwd=remote)
+        utils_for_test.init_git_tree(remote)
         run_git("commit", "--allow-empty", "-minit", cwd=remote)
         run_git("branch", "stable", cwd=remote)
         run_git("tag", "v1.0", cwd=remote)
diff --git a/tests/utils_for_test.py b/tests/utils_for_test.py
new file mode 100644
index 000000000..e162e8666
--- /dev/null
+++ b/tests/utils_for_test.py
@@ -0,0 +1,53 @@
+# Copyright (C) 2026 The Android Open Source Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Various utility code used by tests.
+
+If you want to write a per-test fixture, see conftest.py instead.
+"""
+
+import contextlib
+from pathlib import Path
+import subprocess
+import tempfile
+from typing import Union
+
+import git_command
+
+
+def init_git_tree(path: Union[str, Path]) -> None:
+    """Initialize `path` as a new git repo."""
+    with contextlib.ExitStack() as stack:
+        # Tests need to assume, that main is default branch at init,
+        # which is not supported in config until 2.28.
+        cmd = ["git", "init"]
+        if git_command.git_require((2, 28, 0)):
+            cmd += ["--initial-branch=main"]
+        else:
+            # Use template dir for init.
+            templatedir = stack.enter_context(
+                tempfile.mkdtemp(prefix="git-template")
+            )
+            (Path(templatedir) / "HEAD").write_text("ref: refs/heads/main\n")
+            cmd += ["--template", templatedir]
+        cmd += [path]
+        subprocess.run(cmd, check=True)
+
+
+@contextlib.contextmanager
+def TempGitTree():
+    """Create a new empty git checkout for testing."""
+    with tempfile.TemporaryDirectory(prefix="repo-tests") as tempdir:
+        init_git_tree(tempdir)
+        yield tempdir