diff --git a/cubestat/data.py b/cubestat/data.py
index 2a42d46..86977e6 100644
--- a/cubestat/data.py
+++ b/cubestat/data.py
@@ -13,6 +13,7 @@ def init_group():
 
         self.data = collections.defaultdict(init_group)
 
+    # TODO: UI-related things should be moved out of here
     def get_slice(self, series, indent, h_shift, cols, spacing):
         data_length = len(series) - h_shift if h_shift > 0 else len(series)
         chart_width = cols - 2 * len(spacing) - 2 - len(indent)
diff --git a/cubestat/tests/test_data_manager.py b/cubestat/tests/test_data_manager.py
new file mode 100644
index 0000000..2cb0e26
--- /dev/null
+++ b/cubestat/tests/test_data_manager.py
@@ -0,0 +1,62 @@
+from cubestat.data import DataManager
+
+import unittest
+import collections
+
+
+class TestDataManager(unittest.TestCase):
+    def test_init(self):
+        buffer_size = 10
+        dm = DataManager(buffer_size)
+        self.assertIsInstance(dm.data, collections.defaultdict)
+        self.assertEqual(len(dm.data), 0)
+
+    def test_update(self):
+        buffer_size = 10
+        dm = DataManager(buffer_size)
+        updates = [("group1", "title1", 1), ("group1", "title2", 2), ("group2", "title3", 3)]
+        dm.update(updates)
+        self.assertEqual(len(dm.data), 2)
+        self.assertEqual(len(dm.data["group1"]), 2)
+        self.assertEqual(len(dm.data["group1"]["title1"]), 1)
+        self.assertEqual(len(dm.data["group1"]["title2"]), 1)
+        self.assertEqual(len(dm.data["group2"]), 1)
+        self.assertEqual(len(dm.data["group2"]["title3"]), 1)
+
+    def test_get_slice(self):
+        buffer_size = 10
+        dm = DataManager(buffer_size)
+        series = collections.deque([1, 2, 3, 4, 5, 6, 7, 8, 9, 10], maxlen=buffer_size)
+        indent = "  "
+        h_shift = 2
+        cols = 20
+        spacing = " "
+        expected_slice = [1, 2, 3, 4, 5, 6, 7, 8]
+        self.assertEqual(dm.get_slice(series, indent, h_shift, cols, spacing), expected_slice)
+
+    def test_get_slice_shift(self):
+        buffer_size = 10
+        dm = DataManager(buffer_size)
+        series = collections.deque([1, 2, 3, 4, 5, 6, 7, 8, 9, 10], maxlen=buffer_size)
+        indent = "  "
+        h_shift = 2
+        cols = 10
+        spacing = " "
+        expected_slice = [5, 6, 7, 8]
+        self.assertEqual(dm.get_slice(series, indent, h_shift, cols, spacing), expected_slice)
+
+    def test_data_gen(self):
+        buffer_size = 10
+        dm = DataManager(buffer_size)
+        updates = [("group1", "title1", 1), ("group1", "title2", 2), ("group2", "title3", 3)]
+        dm.update(updates)
+        expected_data = [
+            ("group1", "title1", collections.deque([1], maxlen=buffer_size)),
+            ("group1", "title2", collections.deque([2], maxlen=buffer_size)),
+            ("group2", "title3", collections.deque([3], maxlen=buffer_size)),
+        ]
+        self.assertEqual(list(dm.data_gen()), expected_data)
+
+
+if __name__ == "__main__":
+    unittest.main()