Add taxable social security to the list of Delaware exclusions (#4315)

changelog_entry.yaml

@@ -0,0 +1,4 @@
+- bump: patch
+  changes:
+    fixed:
+    - Add taxable social security to the list of Delaware exclusions.

policyengine_us/parameters/gov/states/de/tax/income/subtractions/subtractions.yaml

@@ -1,12 +1,14 @@
 description: Delaware subtracts these items when calculating state adjusted gross income.
 values:
   2021-01-01:
-    - de_pension_exclusion # (4)
+    - de_pension_exclusion # (3)
+    - taxable_social_security # (4)
     # The elderly or disabled income exclusion is computed separately
     # - de_elderly_or_disabled_income_exclusion # (2)
 
 metadata:
   unit: list
+  period: year
   label: Delaware adjusted gross income subtractions
   references: 
   - title: Delaware Code, § 1106 Modifcations (b)

policyengine_us/tests/policy/baseline/gov/states/de/tax/income/integration.yaml

@@ -154,3 +154,28 @@
         state_fips: 10  # DE
   output:  # expected results from patched TAXSIM35 2024-03-07 version
     de_income_tax: 6585.82
+
+- name: Tax unit with taxsimid 91040 in f21.its.csv and f21.ots.csv
+  absolute_error_margin: 0.01
+  period: 2021
+  input:
+    people:
+      person1:
+        age: 62
+        employment_income: 129_010
+        taxable_interest_income: 11_010
+        taxable_private_pension_income: 6_000
+        social_security_retirement: 24_000
+    tax_units:
+      tax_unit:
+        members: [person1]
+        premium_tax_credit: 0  # not in TAXSIM35
+    spm_units:
+      spm_unit:
+        members: [person1]
+    households:
+      household:
+        members: [person1]
+        state_fips: 10  # DE
+  output:  # expected results from patched TAXSIM35 2024-03-23 version
+    de_income_tax: 7361.32