automatic chunking of zarr archive

I store data in a zarr archive that is not chunked and the resulting zarr archive is chunked.
This may be as simple usage question.
I don't know how to turn this behavior off.

Code sample

Here is minimal example that reproduces the issue:

ds = xr.DataArray(np.ones((200,800))).rename('foo').to_dataset()
print('Initial chunks = {}'.format(ds.foo.chunks))
ds.to_zarr('test.zarr', mode='w')
print('zarr archives contains: {}'.format(os.listdir('test.zarr/foo')))
ds = xr.open_zarr('test.zarr')
print('Final chunks = {}'.format(ds.foo.chunks))

returns:

Initial chunks = None
zarr archives contains: ['.zarray', '.zattrs', '0.0', '0.1', '1.0', '1.1']
Final chunks = ((100, 100), (400, 400))

Expected Output

I would expect the archive to not to be chunked.

Versions

Start by running the minimal example in the issue and inspect the xarray DataArray.to_zarr and open_zarr entry points, along with the reported zarr archive contents. Determine whether automatic chunking is expected behavior and whether the write path supports preserving an unchunked array. Done means the behavior is corrected or the supported way to disable it is clearly established.