@db.register_function(deterministic=True), closes #191

tests/test_register_function.py

@@ -1,3 +1,8 @@
+import pytest
+import sys
+from unittest.mock import MagicMock
+
+
 def test_register_function(fresh_db):
     @fresh_db.register_function
     def reverse_string(s):
@@ -14,3 +19,28 @@ def test_register_function_multiple_arguments(fresh_db):
 
     result = fresh_db.execute("select a_times_b_plus_c(2, 3, 4)").fetchone()[0]
     assert result == 10
+
+
+def test_register_function_deterministic(fresh_db):
+    @fresh_db.register_function(deterministic=True)
+    def to_lower(s):
+        return s.lower()
+
+    result = fresh_db.execute("select to_lower('BOB')").fetchone()[0]
+    assert result == "bob"
+
+
+@pytest.mark.skipif(
+    sys.version_info < (3, 8), reason="deterministic=True was added in Python 3.8"
+)
+def test_register_function_deterministic_registered(fresh_db):
+    fresh_db.conn = MagicMock()
+    fresh_db.conn.create_function = MagicMock()
+
+    @fresh_db.register_function(deterministic=True)
+    def to_lower_2(s):
+        return s.lower()
+
+    fresh_db.conn.create_function.assert_called_with(
+        "to_lower_2", 1, to_lower_2, deterministic=True
+    )