Update tests to verify correct date ranges.

Author: zutigrm

tests/phpunit/integration/Core/Email_Reporting/Initiator_TaskTest.php

@@ -197,4 +197,46 @@ public function test_handle_callback_action_without_subscribers_still_schedules_
 
 		$this->assertEmpty( $posts, 'No email logs should be created when there are no subscribers.' );
 	}
+
+	/**
+	 * @dataProvider data_build_reference_dates_uses_expected_inclusive_period_length
+	 */
+	public function test_build_reference_dates_uses_expected_inclusive_period_length( $frequency, $expected_days ) {
+		$original_timezone_string = get_option( 'timezone_string' );
+		$original_gmt_offset      = get_option( 'gmt_offset' );
+
+		update_option( 'timezone_string', 'UTC' );
+		update_option( 'gmt_offset', 0 );
+
+		try {
+			$timestamp = strtotime( '2026-03-16 00:00:00 UTC' );
+
+			$reference_dates = Initiator_Task::build_reference_dates(
+				$frequency,
+				$timestamp
+			);
+
+			$current_start = new \DateTimeImmutable( $reference_dates['startDate'] );
+			$current_end   = new \DateTimeImmutable( $reference_dates['sendDate'] );
+			$current_days  = (int) $current_start->diff( $current_end )->days + 1;
+
+			$compare_start = new \DateTimeImmutable( $reference_dates['compareStartDate'] );
+			$compare_end   = new \DateTimeImmutable( $reference_dates['compareEndDate'] );
+			$compare_days  = (int) $compare_start->diff( $compare_end )->days + 1;
+
+				$this->assertSame( $expected_days, $current_days, 'Expected current reference range to use inclusive period length.' );
+				$this->assertSame( $expected_days, $compare_days, 'Expected compare reference range to use inclusive period length.' );
+		} finally {
+			update_option( 'timezone_string', $original_timezone_string );
+			update_option( 'gmt_offset', $original_gmt_offset );
+		}
+	}
+
+	public function data_build_reference_dates_uses_expected_inclusive_period_length() {
+		return array(
+			'weekly'    => array( Email_Reporting_Settings::FREQUENCY_WEEKLY, 7 ),
+			'monthly'   => array( Email_Reporting_Settings::FREQUENCY_MONTHLY, 30 ),
+			'quarterly' => array( Email_Reporting_Settings::FREQUENCY_QUARTERLY, 90 ),
+		);
+	}
 }