feat(exceptions): add InvariantError

This exception is to be used when a known invariant is violated.

Signed-off-by: Kevin Morris <kevr@0cost.org>

aurweb/exceptions.py

@@ -86,3 +86,7 @@ class ValidationError(AurwebException):
     def __init__(self, data: Any, *args, **kwargs):
         super().__init__(*args, **kwargs)
         self.data = data
+
+
+class InvariantError(AurwebException):
+    pass

test/test_exceptions.py

@@ -97,3 +97,10 @@ def test_repository_name_exception():
         raise exceptions.InvalidRepositoryNameException("test")
     except exceptions.InvalidRepositoryNameException as exc:
         assert str(exc) == "invalid repository name: test"
+
+
+def test_invariant_error():
+    try:
+        raise exceptions.InvariantError("test")
+    except exceptions.InvariantError as exc:
+        assert str(exc) == "test"