From 1bc1486d914976257b43612e7898330d70f9a499 Mon Sep 17 00:00:00 2001
From: Nikki Gonzales
 <38495263+nikkithelegendarypokemonster@users.noreply.github.com>
Date: Mon, 25 Nov 2024 02:12:37 +0800
Subject: [PATCH 1/2] Initial Commit

---
 .../m_calendar.range.selection.strategy.ts    |  2 +-
 .../dateRangeBox.tests.js                     | 20 +++++++++++++++++++
 2 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/packages/devextreme/js/__internal/ui/calendar/m_calendar.range.selection.strategy.ts b/packages/devextreme/js/__internal/ui/calendar/m_calendar.range.selection.strategy.ts
index b863141abbf8..452b4d7c3b3d 100644
--- a/packages/devextreme/js/__internal/ui/calendar/m_calendar.range.selection.strategy.ts
+++ b/packages/devextreme/js/__internal/ui/calendar/m_calendar.range.selection.strategy.ts
@@ -117,7 +117,7 @@ class CalendarRangeSelectionStrategy extends CalendarSelectionStrategy {
 
     const { currentDate, viewsCount } = this.calendar.option();
     const isAdditionalViewDate = this.calendar._isAdditionalViewDate(currentDate);
-    const firstDateInViews = dateUtils.getFirstMonthDate(dateUtils.addDateInterval(currentDate, 'month', isAdditionalViewDate ? -2 : -1));
+    const firstDateInViews = dateUtils.getFirstMonthDate(dateUtils.addDateInterval(currentDate, 'month', isAdditionalViewDate ? -3 : -2));
     const lastDateInViews = dateUtils.getLastMonthDate(dateUtils.addDateInterval(currentDate, 'month', isAdditionalViewDate ? 1 : viewsCount));
 
     // @ts-expect-error
diff --git a/packages/devextreme/testing/tests/DevExpress.ui.widgets.editors/dateRangeBox.tests.js b/packages/devextreme/testing/tests/DevExpress.ui.widgets.editors/dateRangeBox.tests.js
index 0bcf4db7663d..ee438bf180a6 100644
--- a/packages/devextreme/testing/tests/DevExpress.ui.widgets.editors/dateRangeBox.tests.js
+++ b/packages/devextreme/testing/tests/DevExpress.ui.widgets.editors/dateRangeBox.tests.js
@@ -40,6 +40,7 @@ const CALENDAR_CELL_CLASS = 'dx-calendar-cell';
 const CALENDAR_CONTOURED_CELL_CLASS = 'dx-calendar-contoured-date';
 const APPLY_BUTTON_SELECTOR = '.dx-popup-done.dx-button';
 const CANCEL_BUTTON_SELECTOR = '.dx-popup-cancel.dx-button';
+const CALENDAR_CELL_IN_RANGE_CLASS = 'dx-calendar-cell-in-range';
 const CALENDAR_NAVIGATOR_PREVIOUS_VIEW_CLASS = 'dx-calendar-navigator-previous-view';
 const BUTTON_SELECTOR = '.dx-button';
 const TEXTBOX_SELECTOR = '.dx-textbox';
@@ -52,6 +53,7 @@ const getButtonsContainers = $element => $element.find(`> .${DROP_DOWN_EDITOR_BU
 const getButtons = $element => $element.find(`.${DROP_DOWN_EDITOR_BUTTON_CLASS}`);
 const getClearButton = $element => getButtonsContainers($element).find(`.${CLEAR_BUTTON}`);
 const getPopup = dateBox => dateBox._popup;
+const getCurrentViewInstance = (calendar) => calendar._view;
 
 
 const moduleConfig = {
@@ -1002,6 +1004,24 @@ QUnit.module('Behavior', moduleConfig, () => {
         assert.strictEqual(startDateBox.option('opened'), true, 'startDateBox is opened');
     });
 
+    QUnit.test('Cells in-range should be highlighted when pressing previous button in calendar (T1253076)', function(assert) {
+        this.reinit({
+            value: ['2025-01-01', '2025-12-31'],
+            min: new Date('2025-01-01'),
+            max: new Date('2025-12-31'),
+            multiView: true
+        });
+
+        this.$startDateInput.trigger('click');
+        const calendar = this.getCalendar();
+
+        $(`.${CALENDAR_CELL_CLASS}`).eq(3).trigger('dxclick');
+
+        const $cell = $(getCurrentViewInstance(calendar).$element().find('*[data-value="2025/11/01"]'));
+
+        assert.ok($cell.hasClass(CALENDAR_CELL_IN_RANGE_CLASS));
+    });
+
     ['startDateBox', 'endDateBox'].forEach((dateBoxName) => {
         QUnit.test(`${dateBoxName} should update value on DateRangeBox value change`, function(assert) {
             const newValue = ['2023/04/18', '2023/05/03'];

From cc8d2c7c6350b6ca202080615d2c7042ce7778f2 Mon Sep 17 00:00:00 2001
From: Nikki Gonzales
 <38495263+nikkithelegendarypokemonster@users.noreply.github.com>
Date: Mon, 25 Nov 2024 03:00:51 +0800
Subject: [PATCH 2/2] add assert message

---
 .../tests/DevExpress.ui.widgets.editors/dateRangeBox.tests.js   | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/packages/devextreme/testing/tests/DevExpress.ui.widgets.editors/dateRangeBox.tests.js b/packages/devextreme/testing/tests/DevExpress.ui.widgets.editors/dateRangeBox.tests.js
index ee438bf180a6..d367cd459682 100644
--- a/packages/devextreme/testing/tests/DevExpress.ui.widgets.editors/dateRangeBox.tests.js
+++ b/packages/devextreme/testing/tests/DevExpress.ui.widgets.editors/dateRangeBox.tests.js
@@ -1019,7 +1019,7 @@ QUnit.module('Behavior', moduleConfig, () => {
 
         const $cell = $(getCurrentViewInstance(calendar).$element().find('*[data-value="2025/11/01"]'));
 
-        assert.ok($cell.hasClass(CALENDAR_CELL_IN_RANGE_CLASS));
+        assert.ok($cell.hasClass(CALENDAR_CELL_IN_RANGE_CLASS), 'cell is highlighted');
     });
 
     ['startDateBox', 'endDateBox'].forEach((dateBoxName) => {