don't try running bsddb3 doctests

Author: dstansby

docs/tutorial.rst

@@ -807,21 +807,8 @@ underlying ZIP archive.
 
 Another storage alternative is the :class:`zarr.storage.DBMStore` class, added
 in Zarr version 2.2. This class allows any DBM-style database to be used for
-storing an array or group. Here is an example using a Berkeley DB B-tree
-database for storage (requires `bsddb3
-<https://www.jcea.es/programacion/pybsddb.htm>`_ to be installed):
-
-.. doctest-requires:: bsddb3
-
-    >>> import bsddb3
-    >>> store = zarr.DBMStore('data/example.bdb', open=bsddb3.btopen)
-    >>> root = zarr.group(store=store, overwrite=True)
-    >>> z = root.zeros('foo/bar', shape=(1000, 1000), chunks=(100, 100), dtype='i4')
-    >>> z[:] = 42
-    >>> store.close()
-
-Also added in Zarr version 2.2 is the :class:`zarr.storage.LMDBStore` class which
-enables the lightning memory-mapped database (LMDB) to be used for storing an array or
+storing an array or group. Here is an example using the
+lightning memory-mapped database (LMDB) to be used for storing an array or
 group (requires `lmdb <https://lmdb.readthedocs.io/>`_ to be installed)::
 
     >>> store = zarr.LMDBStore('data/example.lmdb')

zarr/storage.py

@@ -2069,7 +2069,7 @@ class DBMStore(Store):
     <https://www.jcea.es/programacion/pybsddb.htm>`_ package is installed, a
     Berkeley DB database can be used:
 
-    .. doctest-requires:: bsddb3
+    .. doctest-skip::
 
         >>> import bsddb3
         >>> store = zarr.DBMStore('data/array.bdb', open=bsddb3.btopen)