feat: add warnings mode for import/export handlers, commands

can now specify `--warn` for import/export CLI, to get diff email when
changes occur.

this also adds `get_import_handler()` and friends, via app provider.

also declare email settings for the 2 existing importers

tests/test_emails.py

@@ -0,0 +1,81 @@
+# -*- coding: utf-8; -*-
+
+from wuttjamaican.testing import ConfigTestCase
+
+from wuttasync import emails as mod
+from wuttasync.importing import ImportHandler
+from wuttasync.testing import ImportExportWarningTestCase
+
+
+class FromFooToWutta(ImportHandler):
+    pass
+
+
+class TestImportExportWarning(ConfigTestCase):
+
+    def make_setting(self, factory=None):
+        if not factory:
+            factory = mod.ImportExportWarning
+        setting = factory(self.config)
+        return setting
+
+    def test_get_description(self):
+        self.config.setdefault("wutta.app_title", "Wutta Poser")
+        setting = self.make_setting()
+        setting.import_handler_key = "import.to_wutta.from_csv"
+        self.assertEqual(
+            setting.get_description(),
+            "Diff warning email for importing CSV → Wutta Poser",
+        )
+
+    def test_get_default_subject(self):
+        self.config.setdefault("wutta.app_title", "Wutta Poser")
+        setting = self.make_setting()
+        setting.import_handler_key = "import.to_wutta.from_csv"
+        self.assertEqual(setting.get_default_subject(), "Changes for CSV → Wutta Poser")
+
+    def test_get_import_handler(self):
+
+        # nb. typical name pattern
+        class import_to_wutta_from_foo_warning(mod.ImportExportWarning):
+            pass
+
+        # nb. name does not match spec pattern
+        class import_to_wutta_from_bar_blah(mod.ImportExportWarning):
+            pass
+
+        # register our import handler
+        self.config.setdefault(
+            "wuttasync.importing.import.to_wutta.from_foo.handler",
+            "tests.test_emails:FromFooToWutta",
+        )
+
+        # error if spec/key not discoverable
+        setting = self.make_setting(import_to_wutta_from_bar_blah)
+        self.assertRaises(ValueError, setting.get_import_handler)
+
+        # can lookup by name (auto-spec)
+        setting = self.make_setting(import_to_wutta_from_foo_warning)
+        handler = setting.get_import_handler()
+        self.assertIsInstance(handler, FromFooToWutta)
+
+        # can lookup by explicit spec
+        setting = self.make_setting(import_to_wutta_from_bar_blah)
+        setting.import_handler_spec = "tests.test_emails:FromFooToWutta"
+        handler = setting.get_import_handler()
+        self.assertIsInstance(handler, FromFooToWutta)
+
+        # can lookup by explicit key
+        setting = self.make_setting(import_to_wutta_from_bar_blah)
+        setting.import_handler_key = "import.to_wutta.from_foo"
+        handler = setting.get_import_handler()
+        self.assertIsInstance(handler, FromFooToWutta)
+
+
+class TestEmailSettings(ImportExportWarningTestCase):
+
+    def test_import_to_versions_from_wutta_warning(self):
+        self.do_test_preview("import_to_versions_from_wutta_warning")
+
+    def test_import_to_wutta_from_csv_warning(self):
+        self.do_test_preview("import_to_wutta_from_csv_warning")