Add test for DecimalField(precision=0) and raise exception if negative/invalid values are provided

AUTHORS

@@ -261,3 +261,4 @@ that much better:
  * Felix Schultheiß (https://github.com/felix-smashdocs)
  * Jan Stein (https://github.com/janste63)
  * Timothé Perez (https://github.com/AchilleAsh)
+ * oleksandr-l5 (https://github.com/oleksandr-l5)

docs/changelog.rst

@@ -9,6 +9,7 @@ Development
 - (Fill this out as you fix issues and develop your features).
 - EnumField improvements: now `choices` limits the values of an enum to allow
 - Fix deepcopy of EmbeddedDocument #2202
+- Fix error when using precision=0 with DecimalField #2535
 
 Changes in 0.23.1
 ===========

mongoengine/fields.py

@@ -468,6 +468,10 @@ class DecimalField(BaseField):
         self.min_value = min_value
         self.max_value = max_value
         self.force_string = force_string
+
+        if precision < 0 or not isinstance(precision, int):
+            self.error("precision must be a positive integer")
+
         self.precision = precision
         self.rounding = rounding
 
@@ -483,10 +487,12 @@ class DecimalField(BaseField):
         except (TypeError, ValueError, decimal.InvalidOperation):
             return value
         if self.precision > 0:
-            return value.quantize(decimal.Decimal(".%s" % ("0" * self.precision)), rounding=self.rounding)
+            return value.quantize(
+                decimal.Decimal(".%s" % ("0" * self.precision)), rounding=self.rounding
+            )
         else:
             return value.quantize(decimal.Decimal(), rounding=self.rounding)
-        
+
     def to_mongo(self, value):
         if value is None:
             return value

tests/fields/test_decimal_field.py

@@ -118,3 +118,23 @@ class TestDecimalField(MongoDBTestCase):
         assert 2 == Person.objects(money__gt="7").count()
 
         assert 3 == Person.objects(money__gte="7").count()
+
+    def test_precision_0(self):
+        """prevent regression of a bug that was raising an exception when using precision=0"""
+
+        class TestDoc(Document):
+            d = DecimalField(precision=0)
+
+        TestDoc.drop_collection()
+
+        td = TestDoc(d=Decimal("12.00032678131263"))
+        assert td.d == Decimal("12")
+
+    def test_precision_negative_raise(self):
+        """prevent regression of a bug that was raising an exception when using precision=0"""
+        with pytest.raises(
+            ValidationError, match="precision must be a positive integer"
+        ):
+
+            class TestDoc(Document):
+                dneg = DecimalField(precision=-1)