Add test

Author: dstansby

tests/test_api.py

@@ -310,8 +310,12 @@ def test_open_with_mode_r(tmp_path: Path) -> None:
 
 def test_open_with_mode_r_plus(tmp_path: Path) -> None:
     # 'r+' means read/write (must exist)
+    new_store_path = tmp_path / "new_store.zarr"
+    assert not new_store_path.exists(), "Test should operate on non-existent directory"
     with pytest.raises(FileNotFoundError):
-        zarr.open(store=tmp_path, mode="r+")
+        zarr.open(store=new_store_path, mode="r+")
+    assert not new_store_path.exists(), "mode='r+' should not create directory"
+
     zarr.ones(store=tmp_path, shape=(3, 3))
     z2 = zarr.open(store=tmp_path, mode="r+")
     assert isinstance(z2, Array)