chore(tests): add large model test marker to pytest.ini

DEVELOPER.md

@@ -354,6 +354,8 @@ pytest -v -n auto
 Markers can be used to select subsets of tests. Markers provided in `pytest.ini` include:
 
 - `slow`: tests that take longer than a few seconds to complete
+- `repo`: tests that require external model repositories
+- `large`: tests using large models (from the `modflow6-examples` and `modflow6-largetestmodels` repos)
 - `regression`: tests comparing results from multiple versions
 
 Markers can be used with the `-m <marker>` option, and can be applied in boolean combinations with `and`, `or` and `not`. For instance, to run fast tests in parallel, excluding regression tests:
@@ -378,18 +380,24 @@ Tests using models from external repositories can be selected with the `repo` ma
 pytest -v -n auto -m "repo"
 ```
 
-The test scripts can also be run independently:
+The `large` marker is a subset of the `repo` marker. To test models excluded from commit-triggered CI and only run on GitHub Actions nightly:
 
 ```shell
-# Run MODFLOW 6 test models
+pytest -v -n auto -m "large"
+```
+
+Test scripts for external model repositories can also be run independently:
+
+```shell
+# MODFLOW 6 test models
 pytest -v -n auto test_z01_testmodels_mf6.py
 
-# Run MODFLOW 5 to 6 conversion test models
+# MODFLOW 5 to 6 conversion test models
 pytest -v -n auto test_z02_testmodels_mf5to6.py
 
-# Run example models
+# models from modflow6-examples repo
 pytest -v -n auto test_z03_examples.py
 
-# Run large test models
+# models from modflow6-largetestmodels repo
 pytest -v -n auto test_z03_largetestmodels.py
 ```

autotest/pytest.ini

@@ -5,6 +5,7 @@ python_files =
 markers =
     slow: tests taking more than a few seconds to complete
     repo: tests using models loaded from an external repository
+    large: tests using large models (examples and largetestmodels)
     regression: comparing results from different versions
     developmode: tests that should only run with IDEVELOPMODE = 1
     gwf: tests for groundwater flow models