config: Add Config.payment_threshold() method.

This just returns a constant for now, but we know it may need to be
configurable in the future.  Other code can start using this now
to be configurable in the future.

conservancy_beancount/config.py

@@ -14,6 +14,7 @@
 # You should have received a copy of the GNU Affero General Public License
 # along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
+import decimal
 import functools
 import os
 import urllib.parse as urlparse
@@ -86,6 +87,9 @@ class Config:
             and self._dir_or_none(cache_root / name)
         )
 
+    def payment_threshold(self) -> decimal.Decimal:
+        return decimal.Decimal(0)
+
     def repository_path(self) -> Optional[Path]:
         try:
             return Path(os.environ['CONSERVANCY_REPOSITORY'])

tests/test_config.py

@@ -15,6 +15,7 @@
 # along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
 import contextlib
+import decimal
 import os
 import re
 
@@ -281,3 +282,8 @@ def test_cache_path_parent_conflict(tmp_path):
     with update_environ(HOME=tmp_path, XDG_CACHE_DIR=None):
         config = config_mod.Config()
         assert config.cache_dir_path('TESTcache') is None
+
+def test_payment_threshold():
+    threshold = config_mod.Config().payment_threshold()
+    assert threshold == 0
+    assert isinstance(threshold, (int, decimal.Decimal))