Dates: Account for leat year in `getLastPeriod` (https://github.com/woocommerce/woocommerce-admin/pull/6470)

* force end of month

* changelog

plugins/woocommerce-admin/packages/date/CHANGELOG.md

@@ -1,3 +1,7 @@
+# Unreleased
+
+-   Take into account leap year in calculating `getLastPeriod`.
+
 # 2.1.0
 
 -   Update to @wordpress/eslint coding standards.

plugins/woocommerce-admin/packages/date/src/index.js

@@ -148,6 +148,7 @@ export function getLastPeriod( period, compare ) {
 			secondaryEnd = secondaryStart.clone().endOf( period );
 		} else {
 			// Otherwise, use days in primary period to figure out how far to go back
+			// This is necessary for calculating weeks instead of using `endOf`.
 			const daysDiff = primaryEnd.diff( primaryStart, 'days' );
 			secondaryEnd = primaryStart.clone().subtract( 1, 'days' );
 			secondaryStart = secondaryEnd.clone().subtract( daysDiff, 'days' );
@@ -156,6 +157,12 @@ export function getLastPeriod( period, compare ) {
 		secondaryStart = primaryStart.clone().subtract( 1, 'years' );
 		secondaryEnd = primaryEnd.clone().subtract( 1, 'years' );
 	}
+
+	// When the period is month, be sure to force end of month to take into account leap year
+	if ( period === 'month' ) {
+		secondaryEnd = secondaryEnd.clone().endOf( 'month' );
+	}
+
 	return {
 		primaryStart,
 		primaryEnd,

plugins/woocommerce-admin/packages/date/test/index.js

@@ -552,7 +552,7 @@ describe( 'getLastPeriod', () => {
 			).toBe( true );
 		} );
 
-		it.skip( 'should return correct values for previous_year', () => {
+		it( 'should return correct values for previous_year', () => {
 			const dateValue = getLastPeriod( 'month', 'previous_year' );
 
 			const lastMonthkLastYearStart = lastMonthStart
@@ -561,7 +561,6 @@ describe( 'getLastPeriod', () => {
 			const lastMonthkLastYearEnd = lastMonthkLastYearStart
 				.clone()
 				.endOf( 'month' );
-
 			expect(
 				lastMonthkLastYearStart.isSame(
 					dateValue.secondaryStart,