Raise error for empty repositories argument

audb/core/api.py

@@ -38,6 +38,9 @@ def available(
         table with database name as index,
         and backend, host, repository, version as columns
 
+    Raises:
+        ValueError: if ``repositories`` is an empty when provided
+
     Examples:
         >>> df = audb.available(only_latest=True)
         >>> df.loc[["air", "emodb"]]
@@ -63,6 +66,8 @@ def add_database(name: str, version: str, repository: Repository):
 
     if repositories is not None:
         repositories = audeer.to_list(repositories)
+        if not repositories:
+            raise ValueError("'repositories' argument must not be empty when provided")
     else:
         repositories = config.REPOSITORIES
 

tests/test_api.py

@@ -138,6 +138,13 @@ def test_repositories_single(self, repository_index, preprocess_repository):
         # Verify host
         assert df.host.iloc[0] == repository.host
 
+    @pytest.mark.parametrize("repositories", [[], ()])
+    def test_repositories_empty(self, repositories):
+        """Tests empty repositories argument."""
+        expected_error_msg = "'repositories' argument must not be empty when provided"
+        with pytest.raises(ValueError, match=expected_error_msg):
+            audb.available(repositories=repositories)
+
     def test_broken_database(self, repository_with_broken_database):
         """Test having a database only given as a folder."""
         df = audb.available()