Make NI Class 3 a pure input (#1653)

Author: MaxGhenis

policyengine_uk/tests/code_health/test_input_variable_definitions.py

@@ -0,0 +1,34 @@
+from policyengine_uk import CountryTaxBenefitSystem
+
+
+def test_input_variables_do_not_use_defined_for():
+    system = CountryTaxBenefitSystem()
+
+    invalid = {
+        name: variable.defined_for
+        for name, variable in system.variables.items()
+        if variable.is_input_variable() and variable.defined_for is not None
+    }
+
+    assert invalid == {}
+
+
+def test_input_variables_do_not_use_formulas_adds_or_subtracts():
+    system = CountryTaxBenefitSystem()
+
+    invalid = {
+        name: {
+            "formulas": bool(getattr(variable, "formulas", None)),
+            "adds": bool(getattr(variable, "adds", None)),
+            "subtracts": bool(getattr(variable, "subtracts", None)),
+        }
+        for name, variable in system.variables.items()
+        if variable.is_input_variable()
+        and (
+            getattr(variable, "formulas", None)
+            or getattr(variable, "adds", None)
+            or getattr(variable, "subtracts", None)
+        )
+    }
+
+    assert invalid == {}

policyengine_uk/variables/gov/hmrc/national_insurance/class_3/ni_class_3.py

@@ -8,5 +8,4 @@ class ni_class_3(Variable):
     definition_period = YEAR
     value_type = float
     unit = GBP
-    defined_for = "ni_liable"
     reference = "https://www.legislation.gov.uk/ukpga/1992/4/section/13"