Support running testing subset without pygrackle install

Prior to this PR, our test suite would fail unless we had an editable
install. In reality, all test-cases outside of test_models infer the
location of the data files based on the location of the test-files,
which are never part of the wheel.[^1] Therefore, this PR introduces a
few small tweaks to support testing all test-cases outside of
test_models.

Overall, this will be really useful for providing a more rigorous check
of the correctness of our precompiled wheels (see PR grackle-project#320).

[^1]: I know that some packages do ship their test-suites as part of
      the wheel, but that currently makes absolutely no sense for us
      unless we provide users with an easy way to get the datafiles.
      We can always revisit this choice in the future after we merge
      PRs grackle-project#235 & grackle-project#237 (or come up with an equivalent)

Author: mabruzzo

src/python/pygrackle/utilities/model_tests.py

@@ -15,7 +15,6 @@
 import os
 
 from pygrackle import chemistry_data
-from pygrackle.utilities.data_path import grackle_data_dir
 
 model_test_format_version = 1
 
@@ -141,6 +140,10 @@ def get_model_set(model_name, parameter_index, input_index):
     of the Python example scripts.
     """
 
+    # we import this here, rather than at global scope to let us import the
+    # module when we don't have an editable install (for testing purposes)
+    from pygrackle.utilities.data_path import grackle_data_dir
+
     if model_name not in model_sets:
         raise ValueError("Unkown model name: {model_name}.")
 

src/python/tests/test_models.py

@@ -5,11 +5,17 @@
 
 from numpy.testing import assert_allclose
 
+from pygrackle.__config__ import _is_editable_installation
 from pygrackle.utilities.model_tests import model_sets
 from pygrackle.utilities.testing import run_command
 
 from testing_common import grackle_python_dir
 
+pytestmark = pytest.mark.skipif(
+    not _is_editable_installation(),
+    reason="this module currently requires an editable installation"
+)
+
 python_example_dir = os.path.join(grackle_python_dir, "examples")
 
 # collect all of the python-examples and various model configurations into

src/python/tests/testing_common.py

@@ -14,15 +14,8 @@
 
 import os
 
-from pygrackle.__config__ import _is_editable_installation
 from pygrackle.utilities.misc import dirname
 
-if _is_editable_installation():
-    grackle_install_dir = dirname(os.path.abspath(__file__), level=4)
-    grackle_data_dir = os.path.join(grackle_install_dir, "input")
-    grackle_python_dir = os.path.join(grackle_install_dir, "src", "python")
-else:
-    raise RuntimeError(
-        "the current version of pygrackle is not an editable installation. No "
-        "tests that must import from {__file__} can be run"
-    )
+grackle_install_dir = dirname(os.path.abspath(__file__), level=4)
+grackle_data_dir = os.path.join(grackle_install_dir, "input")
+grackle_python_dir = os.path.join(grackle_install_dir, "src", "python")