this variable should not be required (for e3sm)

CIME/SystemTests/err.py

@@ -42,7 +42,7 @@ def _case_two_custom_prerun_action(self):
         expect(rest_cnt >= 1, "No restart files found in {}".format(rest_root))
         rest_dir = restart_list[rest_cnt // 2]
         self._case.restore_from_archive(rest_dir=os.path.join(rest_root, rest_dir))
-        self._case.set_value("DRV_RESTART_POINTER", "rpointer.cpl." + rest_dir)
+        self._set_drv_restart_pointer("rpointer.cpl." + rest_dir)
 
     def _case_two_custom_postrun_action(self):
         # Link back to original case1 name

CIME/tests/test_unit_system_tests_err.py

@@ -0,0 +1,137 @@
+#!/usr/bin/env python3
+
+"""
+Unit tests for ERR system test
+"""
+
+import shutil
+import tempfile
+from pathlib import Path
+from unittest import mock
+
+import pytest
+
+from CIME.SystemTests.err import ERR
+
+
+@pytest.fixture
+def tempdir():
+    """Create a temporary directory for test files."""
+    tmpdir = tempfile.mkdtemp()
+    yield Path(tmpdir)
+    shutil.rmtree(tmpdir, ignore_errors=True)
+
+
+@pytest.fixture
+def caseroot(tempdir):
+    """Create case directory structure."""
+    caseroot = tempdir / "caseroot"
+    caseroot.mkdir(parents=True, exist_ok=True)
+
+    run_dir = caseroot / "run"
+    run_dir.mkdir(parents=True, exist_ok=True)
+
+    return caseroot
+
+
+def create_mock_case(caseroot, drv_restart_pointer=None):
+    """Create a mock case for testing ERR.
+
+    This creates a MagicMock case with the minimum required configuration
+    to instantiate an ERR test object.
+
+    Args:
+        caseroot: Path to the case root directory
+        drv_restart_pointer: Value for DRV_RESTART_POINTER (None if not supported)
+
+    Returns:
+        mock case object
+    """
+    case = mock.MagicMock()
+
+    run_dir = caseroot / "run"
+
+    def get_value(key, *args, **kwargs):
+        values = {
+            "CASEROOT": str(caseroot),
+            "CASEBASEID": "ERR.f19_g16.S",
+            "COMP_INTERFACE": "mct",
+            "DRV_RESTART_POINTER": drv_restart_pointer,
+            "STOP_N": 5,
+            "REST_N": 2,
+            "STOP_OPTION": "ndays",
+            "RUNDIR": str(run_dir),
+            "DOUT_S_ROOT": str(caseroot / "archive"),
+            "NINST": 1,
+            "CASE": "ERR.f19_g16.S",
+            "CIME_OUTPUT_ROOT": str(caseroot.parent),
+        }
+        return values.get(key)
+
+    case.get_value.side_effect = get_value
+    case.get_env.return_value.get_jobs.return_value = [("case.run", {})]
+    case.get_compset_components.return_value = []
+
+    return case
+
+
+def setup_archive_with_restart(caseroot, restart_date="2000-01-01-00000"):
+    """Create archive directory structure with restart files.
+
+    Args:
+        caseroot: Path to case root directory
+        restart_date: Name of restart directory (default: "2000-01-01-00000")
+
+    Returns:
+        Path to the restart directory
+    """
+    rest_dir = caseroot / "archive" / "rest" / restart_date
+    rest_dir.mkdir(parents=True, exist_ok=True)
+    (rest_dir / "rpointer.cpl").touch()
+    return rest_dir
+
+
+@mock.patch(
+    "CIME.SystemTests.system_tests_compare_two.SystemTestsCompareTwo._setup_cases_if_not_yet_done"
+)
+def test_case_two_custom_prerun_action_with_drv_restart_pointer(
+    _setup_cases_if_not_yet_done, caseroot
+):
+    """Test _case_two_custom_prerun_action sets DRV_RESTART_POINTER when supported."""
+    case = create_mock_case(caseroot, drv_restart_pointer="rpointer.cpl")
+    setup_archive_with_restart(caseroot)
+
+    test = ERR(case)
+    test._case1 = mock.MagicMock()
+    test._case1.get_value.return_value = str(caseroot / "archive")
+    test._case = mock.MagicMock()
+
+    test._case_two_custom_prerun_action()
+
+    test._case.set_value.assert_any_call(
+        "DRV_RESTART_POINTER", "rpointer.cpl.2000-01-01-00000"
+    )
+
+
+@mock.patch(
+    "CIME.SystemTests.system_tests_compare_two.SystemTestsCompareTwo._setup_cases_if_not_yet_done"
+)
+def test_case_two_custom_prerun_action_without_drv_restart_pointer(
+    _setup_cases_if_not_yet_done, caseroot
+):
+    """Test _case_two_custom_prerun_action skips DRV_RESTART_POINTER when not supported."""
+    case = create_mock_case(caseroot, drv_restart_pointer=None)
+    setup_archive_with_restart(caseroot)
+
+    test = ERR(case)
+    test._case1 = mock.MagicMock()
+    test._case1.get_value.return_value = str(caseroot / "archive")
+    test._case = mock.MagicMock()
+
+    test._case_two_custom_prerun_action()
+
+    # Verify DRV_RESTART_POINTER was NOT set
+    for call in test._case.set_value.call_args_list:
+        assert (
+            call[0][0] != "DRV_RESTART_POINTER"
+        ), "DRV_RESTART_POINTER should not be set when model doesn't support it"