Skip doctests if optional dependencies are not installed

conftest.py

@@ -36,6 +36,16 @@
 except ImportError:
     collect_ignore.append("dask/dataframe/io/orc/arrow.py")
 
+try:
+    import tiledb  # noqa: F401
+except ImportError:
+    collect_ignore.append("dask/array/tiledb_io.py")
+
+try:
+    import sqlalchemy  # noqa: F401
+except ImportError:
+    collect_ignore.append("dask/dataframe/io/sql.py")
+
 
 def pytest_addoption(parser):
     parser.addoption("--runslow", action="store_true", help="run slow tests")

dask/cache.py

@@ -13,19 +13,19 @@ class Cache(Callback):
     Examples
     --------
 
-    >>> cache = Cache(1e9)
+    >>> cache = Cache(1e9)  # doctest: +SKIP
 
     The cache can be used locally as a context manager around ``compute`` or
     ``get`` calls:
 
-    >>> with cache:                 # doctest: +SKIP
+    >>> with cache:  # doctest: +SKIP
     ...     result = x.compute()
 
     You can also register a cache globally, so that it works for all
     computations:
 
-    >>> cache.register()
-    >>> cache.unregister()
+    >>> cache.register()    # doctest: +SKIP
+    >>> cache.unregister()  # doctest: +SKIP
     """
 
     def __init__(self, cache, *args, **kwargs):

dask/diagnostics/profile.py

@@ -307,8 +307,8 @@ class CacheProfiler(Callback):
     example, the ``nbytes`` function found in ``cachey`` can be used to measure
     the number of bytes in the cache.
 
-    >>> from cachey import nbytes
-    >>> with CacheProfiler(metric=nbytes) as prof:
+    >>> from cachey import nbytes                   # doctest: +SKIP
+    >>> with CacheProfiler(metric=nbytes) as prof:  # doctest: +SKIP
     ...     get(dsk, 'z')
     22