Allow 0 for valuables input

app/means_test/forms/savings.py

@@ -1,10 +1,10 @@
 from flask import session
-from wtforms.validators import InputRequired, NumberRange
+from wtforms.validators import InputRequired
 from app.means_test.fields import MoneyField
 from app.means_test.forms import BaseMeansTestForm
 from app.means_test.widgets import MoneyInput
 from flask_babel import lazy_gettext as _
-from app.means_test.validators import ValidateIfSession
+from app.means_test.validators import ValidateIfSession, NumberRangeAllowZero
 
 
 class SavingsForm(BaseMeansTestForm):
@@ -44,7 +44,7 @@ class SavingsForm(BaseMeansTestForm):
         validators=[
             ValidateIfSession("has_valuables", True),
             InputRequired(message=_("Enter the total of all valuable items over £500")),
-            NumberRange(
+            NumberRangeAllowZero(
                 min=50000,
                 message=_("Enter 0 if you have no valuable items worth over £500 each"),
             ),  # This value is in pence

app/means_test/validators.py

@@ -3,7 +3,7 @@
 from decimal import Decimal, InvalidOperation
 from enum import Enum
 from flask import session
-from wtforms.validators import StopValidation
+from wtforms.validators import StopValidation, NumberRange
 
 
 class ValidateIfType(Enum):
@@ -126,3 +126,13 @@ def validate_currency(value: str | None) -> Decimal | None:
             raise ValueError("Enter a valid amount (maximum 2 decimal places)")
 
         return decimal_value
+
+
+class NumberRangeAllowZero(NumberRange):
+    """Number range validator that allows 0 as a valid input."""
+
+    def __call__(self, form, field):
+        if field.data == 0:
+            return
+
+        super().__call__(form, field)

tests/unit_tests/means_test/test_validators.py

@@ -0,0 +1,58 @@
+from wtforms import Form, IntegerField
+from app.means_test.validators import NumberRangeAllowZero
+
+
+def test_allows_zero():
+    class TestForm(Form):
+        amount = IntegerField("Amount", validators=[NumberRangeAllowZero(min=500)])
+
+    form = TestForm(amount=0)
+    assert form.validate()
+
+
+def test_respects_minimum():
+    class TestForm(Form):
+        amount = IntegerField("Amount", validators=[NumberRangeAllowZero(min=500)])
+
+    form = TestForm(amount=499)
+    assert form.validate() is False
+    assert "Number must be at least 500." in form.amount.errors
+
+    form = TestForm(amount=501)
+    assert form.validate()
+
+
+def test_respects_maximum():
+    class TestForm(Form):
+        amount = IntegerField(
+            "Amount", validators=[NumberRangeAllowZero(min=500, max=1000)]
+        )
+
+    # Test zero (should pass)
+    form = TestForm(amount=0)
+    assert form.validate()
+
+    # Test value above maximum
+    form = TestForm(amount=1001)
+    assert form.validate() is False
+    assert "Number must be between 500 and 1000." in form.amount.errors
+
+    # Test value at maximum
+    form = TestForm(amount=1000)
+    assert form.validate()
+
+
+def test_non_numeric_value():
+    class TestForm(Form):
+        amount = IntegerField("Amount", validators=[NumberRangeAllowZero(min=500)])
+
+    form = TestForm(amount="not_a_number")
+    assert form.validate() is False
+
+
+def test_none_value():
+    class TestForm(Form):
+        amount = IntegerField("Amount", validators=[NumberRangeAllowZero(min=500)])
+
+    form = TestForm(amount=None)
+    assert form.validate() is False