BUG: Fixes should_clean for keep_last=0

tests/data/bundles/test_core.py

@@ -7,7 +7,7 @@ import toolz.curried.operator as op
 
 from zipline.assets.synthetic import make_simple_equity_info
 from zipline.data.bundles import UnknownBundle, from_bundle_ingest_dirname
-from zipline.data.bundles.core import _make_bundle_core
+from zipline.data.bundles.core import _make_bundle_core, BadClean
 from zipline.lib.adjustment import Float64Multiply
 from zipline.pipeline.loaders.synthetic import (
     make_bar_data,
@@ -369,6 +369,26 @@ class BundleCoreTestCase(WithInstanceTmpDir, ZiplineTestCase):
             msg='keep_last=2 did not remove the correct number of ingestions',
         )
 
+        with assert_raises(BadClean):
+            self.clean('bundle', keep_last=-1, environ=self.environ)
+
+        assert_equal(
+            self._list_bundle(),
+            {fourth, fifth},
+            msg='keep_last=-1 removed some ingestions',
+        )
+
+        assert_equal(
+            self.clean('bundle', keep_last=0, environ=self.environ),
+            {fourth, fifth},
+        )
+
+        assert_equal(
+            self._list_bundle(),
+            set(),
+            msg='keep_last=0 did not remove the correct number of ingestions',
+        )
+
     @staticmethod
     def _ts_of_run(run):
         return from_bundle_ingest_dirname(run.rsplit(os.path.sep, 1)[-1])