improve some error messages

src/ldaptool/_main.py

@@ -105,7 +105,7 @@ class _Context:
         try:
             self.config = search.Config.load()
         except Exception as e:
-            raise SystemExit(f"config error: {e}")
+            raise SystemExit(f"config error: {e!r}")
         try:
             self.arguments = arguments_p.from_args(args)
         except decode.InvalidStep as e:

src/ldaptool/search/config.py

@@ -29,7 +29,7 @@ class Realm:
 
     @staticmethod
     def load(name: str, data: typing.Any) -> Realm:
-        assert isinstance(data, dict)
+        assert isinstance(data, dict), f"Realm section isn't a dictionary: {data!r}"
         domain = data.pop("domain")
         servers = data.pop("servers").split()
         forest_root_domain = data.pop("forest_root_domain", domain)
@@ -199,7 +199,7 @@ class Config:
         with open(conf_path) as f:
             data = yaml.safe_load(f)
         assert isinstance(data, dict)
-        assert "realms" in data
+        assert "realms" in data, "Missing realms section in config"
         realms_data = data.pop("realms")
         assert isinstance(realms_data, dict)
         realms = {}