Add tests for cuml & cudf to prevent regresssion.

http://b/144522678

Author: rosbo

tests/test_rapids.py

@@ -0,0 +1,21 @@
+import unittest
+
+import cudf
+from cuml.cluster import DBSCAN
+
+from common import gpu_test
+
+
+class TestRapids(unittest.TestCase):
+    def test_dbscan(self):
+        # Create and populate a GPU DataFrame
+        gdf_float = cudf.DataFrame()
+        gdf_float['0'] = [1.0, 2.0, 5.0]
+        gdf_float['1'] = [4.0, 2.0, 1.0]
+        gdf_float['2'] = [4.0, 2.0, 1.0]
+
+        # Setup and fit clusters
+        dbscan_float = DBSCAN(eps=1.0, min_samples=1)
+        dbscan_float.fit(gdf_float)
+
+        self.assertEqual(3, dbscan_float.labels_.size)