diff --git a/.github/workflows/python-package.yml b/.github/workflows/python-package.yml
index bce778c..f6793a1 100644
--- a/.github/workflows/python-package.yml
+++ b/.github/workflows/python-package.yml
@@ -31,6 +31,11 @@ jobs:
       shell: bash -l {0}
       run: |
         conda env create -n beakerx -f configuration.yml
+    - name: Test BeakerX Base
+      shell: bash -l {0}
+      run: |
+        conda activate beakerx
+        pytest
     - name: Build BeakerX Base
       shell: bash -l {0}
       run: |
diff --git a/beakerx_base/tests/__init__.py b/beakerx_base/tests/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/beakerx_base/tests/test_utils.py b/beakerx_base/tests/test_utils.py
new file mode 100644
index 0000000..2740d2d
--- /dev/null
+++ b/beakerx_base/tests/test_utils.py
@@ -0,0 +1,16 @@
+from email import utils
+import json
+from datetime import date, datetime
+
+import pytest
+from pandas import Timestamp
+
+from ..utils import ObjectEncoder, date_to_int
+
+@pytest.mark.parametrize("obj,expected", (
+    (date(2021, 10, 22), '{"type": "Date", "timestamp": 1634860800000}'),
+    (datetime(2021, 10, 22, 5, 38, 42), '{"type": "Date", "timestamp": 1634881122000}'),
+    (Timestamp(datetime(2021, 10, 22, 5, 38, 42)), '{"type": "Date", "timestamp": 1634881122000}'),
+))
+def test_ObjectEncoder(obj, expected):
+    assert json.dumps(obj, cls=ObjectEncoder) == expected
diff --git a/beakerx_base/utils.py b/beakerx_base/utils.py
index 7f0e11c..8481611 100644
--- a/beakerx_base/utils.py
+++ b/beakerx_base/utils.py
@@ -15,7 +15,7 @@
 import inspect
 import json
 import time
-from datetime import datetime
+from datetime import date, datetime
 from enum import Enum
 
 import numpy as np
@@ -54,13 +54,13 @@ def datetime_to_number(value):
 
 def unix_time(dt):
     if isinstance(dt, Timestamp):
-        j_object = {
-            'type': 'Date',
-            'timestamp': pandas_timestamp_to_int(dt)
-        }
-        return j_object
+        timestamp = pandas_timestamp_to_int(dt)
     else:
-        return date_to_int(dt)
+        timestamp = date_to_int(str(dt))
+    return {
+        'type': 'Date',
+        'timestamp': timestamp
+    }
 
 
 def date_time_2_millis(dt):
@@ -187,18 +187,18 @@ def padYs(g, gMax):
 
 class ObjectEncoder(json.JSONEncoder):
     def default(self, obj):
-        if isinstance(obj, datetime):
-            return self.default(date_time_2_millis(obj))
+        if isinstance(obj, (date, datetime)):
+            return date_time_2_millis(obj)
         elif isinstance(obj, Enum):
-            return self.default(obj.value)
+            return obj.value
         elif isinstance(obj, Color):
-            return self.default(obj.hex())
+            return obj.hex()
         elif isinstance(obj, pd.Series):
-            return self.default(obj.tolist())
+            return obj.tolist()
         elif isinstance(obj, np.ndarray):
-            return self.default(obj.tolist())
+            return obj.tolist()
         elif isinstance(obj, (np.int64, np.bool_)):
-            return self.default(obj.item())
+            return obj.item()
         elif hasattr(obj, "__dict__"):
             d = dict(
                 (key, value)
@@ -218,9 +218,9 @@ def default(self, obj):
                 and not inspect.ismethoddescriptor(value)
                 and not inspect.isroutine(value)
             )
-            return self.default(d)
-        return obj
+            return d
 
+        return json.JSONEncoder.default(self, obj)
 
 class ColorUtils:
     @staticmethod
diff --git a/configuration.yml b/configuration.yml
index 26dfe6e..aef6e12 100644
--- a/configuration.yml
+++ b/configuration.yml
@@ -6,3 +6,4 @@ dependencies:
   - pandas
   - python=3.7.5
   - pytz
+  - pytest