chore(tests): automatic submodule init

In order to reduce the burden for new contributors, I have added a
pytest fixture which checks that the submodule has been created. If it
is not, it will try and run `git submodule init`.

Signed-off-by: JP-Ellis <[email protected]>

tests/v3/compatibility-suite/__init__.py

@@ -0,0 +1,3 @@
+"""
+Compatibility suite tests.
+"""

tests/v3/compatibility-suite/conftest.py

@@ -0,0 +1,30 @@
+"""
+Pytest configuration.
+
+As the compatibility suite makes use of a submodule, we need to make sure the
+submodule has been initialized before running the tests.
+"""
+
+import shutil
+import subprocess
+from pathlib import Path
+
+import pytest
+
+
+@pytest.fixture(scope="session", autouse=True)
+def _submodule_init() -> None:
+    """Initialize the submodule."""
+    # Locate the git execute
+    submodule_dir = Path(__file__).parent / "definition"
+    if submodule_dir.is_dir():
+        return
+
+    git_exec = shutil.which("git")
+    if git_exec is None:
+        msg = (
+            "Submodule not initialized and git executable not found."
+            " Please initialize the submodule with `git submodule init`."
+        )
+        raise RuntimeError(msg)
+    subprocess.check_call([git_exec, "submodule", "init"])  # noqa: S603