test: add NotBijection test

hugr-py/tests/test_bimap.py

@@ -1,4 +1,6 @@
-from hugr.utils import BiMap
+import pytest
+
+from hugr.utils import BiMap, NotBijection
 
 
 def test_insert_left() -> None:
@@ -61,3 +63,19 @@ def test_existing_key() -> None:
     assert bimap.get_left(1) == "b"
 
     assert bimap.get_right("a") is None
+
+
+def test_bimap_init():
+    # Test with empty initial map
+    bm = BiMap()
+    assert len(bm) == 0
+
+    # Test with non-empty initial map
+    initial_map = {"a": 1, "b": 2}
+    bm = BiMap(initial_map)
+    assert len(bm) == 2
+
+    # Test with non-bijection initial map
+    invalid_map = {"a": 1, "b": 1}
+    with pytest.raises(NotBijection):
+        bm = BiMap(invalid_map)