feat: add problem checks + handler feature

the basic idea is to run nightly checks and send email if problems are
found.  it should also support variations on that theme,
e.g. configuring a check to only run on certain weekdays.

tests/cli/test_problems.py

@@ -0,0 +1,53 @@
+# -*- coding: utf-8; -*-
+
+from unittest.mock import Mock, patch
+
+from wuttjamaican.testing import ConfigTestCase
+from wuttjamaican.cli import problems as mod
+from wuttjamaican.problems import ProblemHandler, ProblemCheck
+
+
+class FakeCheck(ProblemCheck):
+    system_key = 'wuttatest'
+    problem_key = 'fake_check'
+    title = "Fake problem check"
+
+
+class TestProblems(ConfigTestCase):
+
+    def test_basic(self):
+        ctx = Mock()
+        ctx.parent.wutta_config = self.config
+
+        # nb. avoid printing to console
+        with patch.object(mod.rich, 'print') as rich_print:
+
+            # nb. use fake check
+            with patch.object(ProblemHandler, 'get_all_problem_checks', return_value=[FakeCheck]):
+
+                with patch.object(ProblemHandler, 'run_problem_checks') as run_problem_checks:
+
+                    # list problem checks
+                    orig_organize = ProblemHandler.organize_problem_checks
+                    def mock_organize(checks):
+                        return orig_organize(None, checks)
+                    with patch.object(ProblemHandler, 'organize_problem_checks', side_effect=mock_organize) as organize_problem_checks:
+                        mod.problems(ctx, list_checks=True)
+                        organize_problem_checks.assert_called_once_with([FakeCheck])
+                        run_problem_checks.assert_not_called()
+
+                    # warning if unknown system key requested
+                    rich_print.reset_mock()
+                    # nb. just --list for convenience
+                    # note that since we also specify invalid --system, no checks will
+                    # match and hence nothing significant will be printed to stdout
+                    mod.problems(ctx, list_checks=True, systems=['craziness'])
+                    rich_print.assert_called_once()
+                    self.assertEqual(len(rich_print.call_args.args), 1)
+                    self.assertIn("No problem reports exist for system", rich_print.call_args.args[0])
+                    self.assertEqual(len(rich_print.call_args.kwargs), 0)
+                    run_problem_checks.assert_not_called()
+
+                    # run problem checks
+                    mod.problems(ctx)
+                    run_problem_checks.assert_called_once_with([FakeCheck])