diff --git a/test_bitmask.py b/test_bitmask.py
new file mode 100644
index 0000000..18e5d89
--- /dev/null
+++ b/test_bitmask.py
@@ -0,0 +1,175 @@
+from bitmask import Bitmask
+from enum import IntFlag
+import unittest
+
+class Desc(IntFlag):
+    SMALL = 1
+    ROUND = 1 << 1
+    FUNKY = 1 << 2
+
+class TestBitmask(unittest.TestCase):
+    def setUp(self):
+        """Initialize `Bitmask` instances for testing."""
+        self.bmask = Bitmask(Desc, Desc.SMALL, Desc.FUNKY)
+        self.bmask2 = Bitmask(Desc, Desc.ROUND)
+        self.bmask3 = Bitmask(Desc, Desc.ROUND)
+        self.bmask_empty = Bitmask(Desc)
+
+    def test_eq(self):
+        """Test equality."""
+        self.assertEqual(self.bmask2, self.bmask3)
+        self.assertNotEqual(self.bmask, self.bmask3)
+        self.assertNotEqual(self.bmask, self.bmask_empty)
+        self.assertNotEqual(self.bmask, Desc.SMALL)
+        self.assertNotEqual(self.bmask, Desc.ROUND)
+        self.assertNotEqual(self.bmask_empty, Desc.ROUND)
+
+    def test_repr(self):
+        """Test __repr__."""
+        self.assertEqual(eval(repr(self.bmask)), self.bmask)
+        self.assertEqual(eval(repr(self.bmask_empty)), self.bmask_empty)
+
+    def test_add(self):
+        """Test the `Bitmask.add()` method."""
+        self.bmask.add(Desc.ROUND)
+        self.assertEqual(
+            self.bmask,
+            Bitmask(Desc, Desc.SMALL, Desc.FUNKY, Desc.ROUND)
+        )
+
+        self.bmask_empty.add(Desc.ROUND)
+        self.bmask_empty.add(Desc.ROUND)
+        self.assertEqual(
+            self.bmask_empty,
+            Bitmask(Desc, Desc.ROUND)
+        )
+
+    def test_add_operator(self):
+        """Test the + operator."""
+        self.assertEqual(
+            self.bmask + Desc.ROUND,
+            Bitmask(Desc, Desc.SMALL, Desc.FUNKY, Desc.ROUND)
+        )
+        self.assertEqual(
+            self.bmask_empty + Desc.ROUND,
+            Bitmask(Desc, Desc.ROUND)
+        )
+        # Test `__radd__`.
+        self.assertEqual(
+            Desc.ROUND + self.bmask,
+            Bitmask(Desc, Desc.SMALL, Desc.FUNKY, Desc.ROUND)
+        )
+        # Test combining bitmasks
+        self.assertEqual(
+            self.bmask + self.bmask2 + self.bmask3,
+            Bitmask(Desc, Desc.SMALL, Desc.FUNKY, Desc.ROUND)
+        )
+
+    def test_remove(self):
+        """Test the `Bitmask.remove()` method."""
+        self.bmask.remove(Desc.SMALL)
+        self.assertEqual(
+            self.bmask,
+            Bitmask(Desc, Desc.FUNKY)
+        )
+        with self.assertRaises(KeyError):
+            self.bmask.remove(Desc.SMALL)
+        with self.assertRaises(KeyError):
+            self.bmask_empty.remove(Desc.SMALL)
+    
+    def test_discard(self):
+        """Test the `Bitmask.discard()` method."""
+        self.bmask.discard(Desc.SMALL)
+        self.assertEqual(
+            self.bmask,
+            Bitmask(Desc, Desc.FUNKY)
+        )
+        self.bmask.discard(Desc.SMALL)
+        self.assertEqual(
+            self.bmask,
+            Bitmask(Desc, Desc.FUNKY)
+        )
+        self.bmask_empty.discard(Desc.SMALL)
+        self.assertEqual(
+            self.bmask_empty,
+            Bitmask(Desc)
+        )
+
+    def test_value(self):
+        """Ensure Bitmask.value lines up with the state."""
+        self.assertEqual(self.bmask.value, 5)
+        self.bmask.add(Desc.ROUND)
+        self.assertEqual(self.bmask.value, 7)
+
+        self.assertEqual(self.bmask_empty.value, 0)
+
+        # Setting values directly
+        self.bmask.value = 0
+        self.assertEqual(
+            self.bmask,
+            Bitmask(Desc)
+        )
+        self.bmask.value = 1
+        self.assertEqual(
+            self.bmask,
+            Bitmask(Desc, Desc.SMALL)
+        )
+        with self.assertRaises(TypeError):
+            self.bmask.value = 1j
+        with self.assertRaises(TypeError):
+            self.bmask.value = 2.5
+        with self.assertRaises(TypeError):
+            self.bmask.value = -1
+
+    def test_contains(self):
+        """Test `flag in mask` check."""
+        self.assertIn(Desc.FUNKY, self.bmask)
+        self.assertIn(Desc.SMALL, self.bmask)
+        self.assertNotIn(Desc.ROUND, self.bmask)
+        self.assertNotIn(Desc.ROUND, self.bmask_empty)
+        with self.assertRaises(TypeError):
+            self.bmask in self.bmask
+
+    def test_iter(self):
+        """Test iteration."""
+        self.assertEqual(
+            [i for i in self.bmask],
+            [Desc.SMALL, Desc.FUNKY]
+        )
+
+    def test_str(self):
+        """Test string conversion."""
+        self.assertEqual(
+            str(self.bmask),
+            "SMALL|FUNKY"
+        )
+        self.bmask.add(Desc.ROUND)
+        self.assertEqual(
+            str(self.bmask),
+            "SMALL|ROUND|FUNKY"
+        )
+
+        self.assertEqual(
+            str(self.bmask_empty),
+            "0"
+        )
+        self.bmask_empty.add(Desc.ROUND)
+        self.assertEqual(
+            str(self.bmask_empty),
+            "ROUND"
+        )
+
+    def test_int(self):
+        """Test int conversion."""
+        self.assertEqual(
+            int(self.bmask),
+            self.bmask.value
+        )
+        self.bmask.value = 4
+        self.assertEqual(
+            int(self.bmask),
+            self.bmask.value
+        )
+
+if __name__ == '__main__':
+    unittest.main()