test: cover month snapshot, deviation states, and per-month target

Service tests assert that create_month produces origin fields matching
the budget, that edits flip deviation_state to edited, that added rows
are new_in_month, and that a budget entry deleted after snapshot leaves
the month entry unchanged. Route tests exercise the create flow,
applied updates, name edits producing the modified tag, per-month
target isolation, and the malformed-year-month 404.

Refs #3

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/test_month_routes.py

@@ -0,0 +1,139 @@
+from __future__ import annotations
+
+
+def _seed_budget_via_api(client):
+    client.post(
+        "/sections/income/entries",
+        data={"name": "Paycheck", "amount": "2500.00"},
+    )
+    client.post(
+        "/sections/fixed_bill/entries",
+        data={"name": "Rent", "amount": "1200.00"},
+    )
+    client.post(
+        "/sections/debt_minimum/entries",
+        data={"name": "Card A", "amount": "40.00"},
+    )
+
+
+def test_missing_month_renders_create_flow(client):
+    response = client.get("/month/2026-04")
+    assert response.status_code == 200
+    assert "No snapshot yet" in response.text
+    assert 'hx-post="/month/2026-04/create"' in response.text
+
+
+def test_create_month_redirects_via_htmx(client):
+    _seed_budget_via_api(client)
+    response = client.post("/month/2026-04/create")
+    assert response.status_code == 204
+    assert response.headers.get("hx-redirect") == "/month/2026-04"
+
+
+def test_created_month_renders_snapshot(client):
+    _seed_budget_via_api(client)
+    client.post("/month/2026-04/create")
+    response = client.get("/month/2026-04")
+    assert response.status_code == 200
+    assert "Paycheck" in response.text
+    assert "Rent" in response.text
+    assert "Card A" in response.text
+    # totals: applied / planned
+    assert "$2500.00" in response.text
+    assert "$1200.00" in response.text
+
+
+def test_applied_update_returns_section_partial(client):
+    _seed_budget_via_api(client)
+    client.post("/month/2026-04/create")
+    # fetch month page, identify rent month_entry id = 2 (after income id 1)
+    response = client.post(
+        "/month/2026-04/entries/2", data={"applied": "1200.00"}
+    )
+    assert response.status_code == 200
+    # rent is in fixed_bill section; total_applied should now include 1200
+    assert 'id="section-fixed_bill"' in response.text
+    # two $1200.00 occurrences: total_applied and planned (same amount)
+    assert response.text.count("$1200.00") >= 2
+
+
+def test_name_edit_flips_to_modified(client):
+    _seed_budget_via_api(client)
+    client.post("/month/2026-04/create")
+    response = client.post(
+        "/month/2026-04/entries/2", data={"name": "Rent (April)"}
+    )
+    assert response.status_code == 200
+    assert "state-edited" in response.text
+    assert 'class="tag tag-edited">modified' in response.text
+
+
+def test_add_new_entry_within_month_is_marked_new(client):
+    _seed_budget_via_api(client)
+    client.post("/month/2026-04/create")
+    response = client.post(
+        "/month/2026-04/sections/other/entries",
+        data={"name": "Gift", "planned": "50.00"},
+    )
+    assert response.status_code == 200
+    assert "state-new_in_month" in response.text
+    assert "new this month" in response.text
+
+
+def test_delete_month_entry(client):
+    _seed_budget_via_api(client)
+    client.post("/month/2026-04/create")
+    response = client.delete("/month/2026-04/entries/2")
+    assert response.status_code == 200
+    assert "Rent" not in response.text
+
+
+def test_delete_month_debt_minimum_updates_target(client):
+    _seed_budget_via_api(client)
+    client.post("/month/2026-04/create")
+    # Card A is entry id 3 in the month snapshot
+    response = client.delete("/month/2026-04/entries/3")
+    assert response.status_code == 200
+    assert "section-debt_target" in response.text
+    assert "No target selected" in response.text
+
+
+def test_set_month_target(client):
+    _seed_budget_via_api(client)
+    client.post(
+        "/sections/debt_minimum/entries",
+        data={"name": "Card B", "amount": "60.00"},
+    )
+    client.post("/month/2026-04/create")
+    # Card B is month_entry id 4
+    response = client.post(
+        "/month/2026-04/target", data={"month_entry_id": "4"}
+    )
+    assert response.status_code == 200
+    assert "Card B" in response.text
+
+
+def test_month_target_isolated_between_months(client):
+    _seed_budget_via_api(client)
+    client.post(
+        "/sections/debt_minimum/entries",
+        data={"name": "Card B", "amount": "60.00"},
+    )
+    client.post("/month/2026-04/create")
+    client.post("/month/2026-05/create")
+    # Change April target to Card B (month_entry id 4 within April)
+    client.post("/month/2026-04/target", data={"month_entry_id": "4"})
+    may_page = client.get("/month/2026-05")
+    # May still points at Card A (copied from budget)
+    assert "Card A" in may_page.text
+
+
+def test_malformed_year_month_returns_404(client):
+    response = client.get("/month/2026-13")
+    assert response.status_code == 404
+
+
+def test_budget_page_shows_month_nav(client):
+    response = client.get("/")
+    assert response.status_code == 200
+    assert "This month" in response.text

tests/test_month_service.py

@@ -0,0 +1,148 @@
+from __future__ import annotations
+
+from decimal import Decimal
+
+import pytest
+
+from quartermaster import month_service, service
+from quartermaster.models import Section
+
+
+def _seed_budget(db):
+    income = service.add_entry(db, Section.income, "Paycheck", Decimal("2500.00"))
+    rent = service.add_entry(
+        db, Section.fixed_bill, "Rent", Decimal("1200.00")
+    )
+    card_a = service.add_entry(
+        db, Section.debt_minimum, "Card A", Decimal("40.00")
+    )
+    card_b = service.add_entry(
+        db, Section.debt_minimum, "Card B", Decimal("60.00")
+    )
+    service.set_debt_target(db, card_a.id)
+    return income, rent, card_a, card_b
+
+
+def test_valid_year_month():
+    assert month_service.valid_year_month("2026-04")
+    assert month_service.valid_year_month("2026-12")
+    assert not month_service.valid_year_month("2026-00")
+    assert not month_service.valid_year_month("2026-13")
+    assert not month_service.valid_year_month("26-04")
+    assert not month_service.valid_year_month("2026/04")
+
+
+def test_shift_year_month_rolls_years():
+    assert month_service.shift_year_month("2026-12", 1) == "2027-01"
+    assert month_service.shift_year_month("2026-01", -1) == "2025-12"
+    assert month_service.shift_year_month("2026-04", 0) == "2026-04"
+    assert month_service.shift_year_month("2026-04", 12) == "2027-04"
+
+
+def test_create_month_snapshots_budget(db):
+    income, rent, card_a, card_b = _seed_budget(db)
+    month = month_service.create_month(db, "2026-04")
+    assert month.year_month == "2026-04"
+    assert len(month.entries) == 4
+    by_source = {e.source_entry_id: e for e in month.entries}
+    assert by_source[income.id].planned == Decimal("2500.00")
+    assert by_source[income.id].origin_name == "Paycheck"
+    assert by_source[income.id].origin_planned == Decimal("2500.00")
+    assert by_source[income.id].applied == Decimal("0.00")
+    assert by_source[rent.id].section == Section.fixed_bill
+    assert month.target is not None
+    assert month.target.entry is not None
+    assert month.target.entry.source_entry_id == card_a.id
+
+
+def test_create_month_idempotent(db):
+    _seed_budget(db)
+    first = month_service.create_month(db, "2026-04")
+    second = month_service.create_month(db, "2026-04")
+    assert first.id == second.id
+
+
+def test_create_month_rejects_bad_year_month(db):
+    with pytest.raises(ValueError):
+        month_service.create_month(db, "2026-00")
+
+
+def test_deviation_state_reflects_edits(db):
+    _seed_budget(db)
+    month = month_service.create_month(db, "2026-04")
+    rent = next(e for e in month.entries if e.origin_name == "Rent")
+    assert month_service.deviation_state(rent) == month_service.DeviationState.unchanged
+
+    month_service.update_month_entry(
+        db, month, rent.id, planned=Decimal("1300.00")
+    )
+    rent = next(e for e in month.entries if e.id == rent.id)
+    assert month_service.deviation_state(rent) == month_service.DeviationState.edited
+
+
+def test_added_row_is_new_in_month(db):
+    _seed_budget(db)
+    month = month_service.create_month(db, "2026-04")
+    extra = month_service.add_month_entry(
+        db, month, Section.other, "Surprise", Decimal("20.00")
+    )
+    assert extra.origin_name is None
+    assert month_service.deviation_state(extra) == (
+        month_service.DeviationState.new_in_month
+    )
+
+
+def test_applied_update_changes_totals(db):
+    _seed_budget(db)
+    month = month_service.create_month(db, "2026-04")
+    rent = next(e for e in month.entries if e.origin_name == "Rent")
+    month_service.update_month_entry(
+        db, month, rent.id, applied=Decimal("1200.00")
+    )
+    view = month_service.section_view(month, Section.fixed_bill, "Fixed")
+    assert view.total_applied == Decimal("1200.00")
+    assert view.total_planned == Decimal("1200.00")
+
+
+def test_per_month_target_is_isolated(db):
+    _seed_budget(db)
+    april = month_service.create_month(db, "2026-04")
+    may = month_service.create_month(db, "2026-05")
+    april_b = next(
+        e for e in april.entries
+        if e.section == Section.debt_minimum and e.origin_name == "Card B"
+    )
+    month_service.set_month_target(db, april, april_b.id)
+    april_target = month_service.get_month_target(db, april)
+    may_target = month_service.get_month_target(db, may)
+    assert april_target.entry is not None
+    assert april_target.entry.origin_name == "Card B"
+    assert may_target.entry is not None
+    assert may_target.entry.origin_name == "Card A"
+
+
+def test_delete_month_entry_returns_section(db):
+    _seed_budget(db)
+    month = month_service.create_month(db, "2026-04")
+    rent = next(e for e in month.entries if e.origin_name == "Rent")
+    result = month_service.delete_month_entry(db, month, rent.id)
+    assert result == Section.fixed_bill
+    db.refresh(month)
+    remaining = [
+        e for e in month.entries if e.section == Section.fixed_bill
+    ]
+    assert remaining == []
+
+
+def test_budget_entry_deleted_after_snapshot_leaves_month_intact(db):
+    _seed_budget(db)
+    month = month_service.create_month(db, "2026-04")
+    # remove budget-side rent; month-side rent should still render unchanged
+    budget_rent = service.list_entries(db, Section.fixed_bill)[0]
+    service.delete_entry(db, budget_rent.id)
+    db.expire_all()
+    month_rent = next(e for e in month.entries if e.origin_name == "Rent")
+    assert month_rent.source_entry_id is None
+    assert month_service.deviation_state(month_rent) == (
+        month_service.DeviationState.unchanged
+    )