diff --git a/lib/tests/test_util.py b/lib/tests/test_util.py
new file mode 100644
index 00000000..f0da88be
--- /dev/null
+++ b/lib/tests/test_util.py
@@ -0,0 +1,19 @@
+import unittest
+from lib.util import format_satoshis
+
+class TestUtil(unittest.TestCase):
+
+    def test_format_satoshis(self):
+        result = format_satoshis(1234)
+        expected = "0.00001234"
+        self.assertEqual(expected, result)
+
+    def test_format_satoshis_diff_positive(self):
+        result = format_satoshis(1234, is_diff=True)
+        expected = "+0.00001234"
+        self.assertEqual(expected, result)
+
+    def test_format_satoshis_diff_negative(self):
+        result = format_satoshis(-1234, is_diff=True)
+        expected = "-0.00001234"
+        self.assertEqual(expected, result)