Fix NT Picnic Day: first Monday of August (DEV-30999)

[mikkotansc]

Problem

NT Picnic Day (au_nt) is defined with a hardcoded date:

picnic_day_from_2025 => Date.civil(year, 8, 4)

Picnic Day is legislated as the first Monday of August. The hardcoded 4th only coincidentally matched reality in 2025 (4 Aug 2025 was the first Monday). It resolves incorrectly for:

Year	Was (hardcoded)	Correct (1st Mon Aug)
2025	Mon 4 Aug ✅	Mon 4 Aug
2026	Tue 4 Aug ❌	Mon 3 Aug
2027	Wed 4 Aug ❌	Mon 2 Aug

This feeds ShiftCare's auto-populated public holidays → payroll/timesheets for all NT accounts. Reported via escalation DEV-30999 (account Being Mentors NT).

Fix

Compute the first Monday of August using DateCalculatorFactory.day_of_month_calculator, mirroring the existing qld_queens_bday_october definition in the same file. The year >= 2025 gate is preserved, so pre-2025 historical data is unchanged.

DateCalculatorFactory.day_of_month_calculator.call(year, 8, :first, :monday)

Tests

Added regression assertions to au.yaml (tests: block) and regenerated test/defs/test_defs_au.rb:

assert_equal "Picnic Day", Date.civil(2025, 8, 4).holidays(:au_nt)[0][:name]
assert_equal "Picnic Day", Date.civil(2026, 8, 3).holidays(:au_nt)[0][:name]
assert_equal "Picnic Day", Date.civil(2027, 8, 2).holidays(:au_nt)[0][:name]
assert_equal [], Date.civil(2026, 8, 4).holidays(:au_nt)   # the old hardcoded-4th bug

The AU defs test passes (109 assertions, 0 failures). The 8 pre-existing suite failures are unrelated US/CA definition drift (identical count on the base branch).

Notes

• Base branch is holidays-april-16-2025 (the branch the app's Gemfile pins), following PR Add ANZAC Day 2026 observed holiday for NSW (April 27) #13.
• Diff is scoped to au.yaml, au.rb, test/defs/test_defs_au.rb. Unrelated rake generate churn in REGIONS.rb/nz.rb was excluded.
• Follow-up (separate): Melbourne Cup missing for VIC-Melbourne accounts — likely an app-side region-mapping issue, not this gem.

[Copilot]

Pull request overview

Updates the Northern Territory (AU-NT) “Picnic Day” holiday definition so it correctly follows legislation (first Monday of August) instead of a hardcoded August 4th date, preventing incorrect holiday population in downstream payroll/timesheet flows.

Changes:

• Replaced the fixed Date.civil(year, 8, 4) computation with a “first Monday of August” calculation for year >= 2025.
• Added regression test cases for 2025–2027 and a negative assertion for the previously-buggy 2026-08-04 case in both the YAML tests block and the generated AU defs test file.
• Regenerated the AU generated definitions to reflect the updated custom method.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
definitions/au.yaml	Updates picnic_day_from_2025 to compute the first Monday of August and adds regression assertions in the YAML tests: block.
lib/generated_definitions/au.rb	Regenerates the AU custom method implementation to use DateCalculatorFactory.day_of_month_calculator for Picnic Day.
test/defs/test_defs_au.rb	Adds explicit regression assertions for Picnic Day dates (2025–2027) and verifies the old hardcoded date no longer returns a holiday.

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