diff --git a/js/src/calendar.js b/js/src/calendar.js
index db0df4cc0..a3918ece7 100644
--- a/js/src/calendar.js
+++ b/js/src/calendar.js
@@ -920,11 +920,11 @@ class Calendar extends BaseComponent {
         return
       }
 
-      if (data[config] === undefined || config.startsWith('_') || config === 'constructor') {
+      if (typeof data[config] === 'undefined') {
         throw new TypeError(`No method named "${config}"`)
       }
 
-      data[config](this)
+      data[config]()
     })
   }
 }
diff --git a/js/src/range-slider.js b/js/src/range-slider.js
index 7f1ca0533..75fa61670 100644
--- a/js/src/range-slider.js
+++ b/js/src/range-slider.js
@@ -357,7 +357,7 @@ class RangeSlider extends BaseComponent {
       }
     }
 
-    return null
+    return '1rem'
   }
 
   _positionTooltip(tooltip, input) {
diff --git a/js/tests/unit/calendar.spec.js b/js/tests/unit/calendar.spec.js
new file mode 100644
index 000000000..626a993ed
--- /dev/null
+++ b/js/tests/unit/calendar.spec.js
@@ -0,0 +1,301 @@
+/* eslint-env jasmine */
+
+import Calendar from '../../src/calendar.js'
+import {
+  getFixture, clearFixture, createEvent, jQueryMock
+} from '../helpers/fixture.js'
+import EventHandler from '../../src/dom/event-handler.js'
+
+describe('Calendar', () => {
+  let fixtureEl
+
+  beforeAll(() => {
+    fixtureEl = getFixture()
+  })
+
+  afterEach(() => {
+    clearFixture()
+  })
+
+  describe('Default', () => {
+    it('should return plugin default config', () => {
+      expect(Calendar.Default).toEqual(jasmine.any(Object))
+    })
+  })
+
+  describe('DefaultType', () => {
+    it('should return plugin default type config', () => {
+      expect(Calendar.DefaultType).toEqual(jasmine.any(Object))
+    })
+  })
+
+  describe('NAME', () => {
+    it('should return plugin NAME', () => {
+      expect(Calendar.NAME).toEqual('calendar')
+    })
+  })
+
+  describe('constructor', () => {
+    it('should create a Calendar instance with default config if no config is provided', () => {
+      fixtureEl.innerHTML = '<div></div>'
+
+      const div = fixtureEl.querySelector('div')
+      const calendar = new Calendar(div)
+
+      expect(calendar).toBeInstanceOf(Calendar)
+      expect(calendar._config).toBeDefined()
+      expect(calendar._element).toEqual(div)
+    })
+
+    it('should allow overriding default config', () => {
+      fixtureEl.innerHTML = '<div></div>'
+
+      const div = fixtureEl.querySelector('div')
+      const calendar = new Calendar(div, {
+        locale: 'fr',
+        calendars: 2,
+        selectionType: 'month'
+      })
+
+      expect(calendar._config.locale).toEqual('fr')
+      expect(calendar._config.calendars).toEqual(2)
+      expect(calendar._config.selectionType).toEqual('month')
+    })
+
+    it('should set `_view` based on `selectionType`', () => {
+      fixtureEl.innerHTML = '<div></div>'
+
+      const div = fixtureEl.querySelector('div')
+      const calendar = new Calendar(div, {
+        selectionType: 'year'
+      })
+
+      expect(calendar._view).toEqual('years')
+    })
+
+    it('should properly create the initial markup for days view', () => {
+      fixtureEl.innerHTML = '<div></div>'
+
+      const div = fixtureEl.querySelector('div')
+      new Calendar(div) // eslint-disable-line no-new
+
+      // Check if .calendar container is created
+      expect(div.querySelector('.calendar')).not.toBeNull()
+
+      // Check if .calendar-nav exists
+      expect(div.querySelector('.calendar-nav')).not.toBeNull()
+
+      // Check if a table with <thead> is created (days view)
+      expect(div.querySelector('.calendar table thead')).not.toBeNull()
+      expect(div.querySelector('.calendar table tbody')).not.toBeNull()
+    })
+  })
+
+  describe('update', () => {
+    it('should clear the calendar HTML and create a new one', () => {
+      fixtureEl.innerHTML = '<div></div>'
+
+      const div = fixtureEl.querySelector('div')
+      const calendar = new Calendar(div)
+      const oldHtml = div.innerHTML
+
+      calendar.update({
+        selectionType: 'month'
+      })
+
+      expect(div.innerHTML).not.toEqual(oldHtml)
+      // Now we should see the months view
+      expect(div.querySelector('.calendar table thead')).toBeNull()
+      expect(div.querySelector('.calendar table tbody')).not.toBeNull()
+      expect(div.querySelector('.month')).not.toBeNull()
+    })
+
+    it('should use the new config object after update', () => {
+      fixtureEl.innerHTML = '<div></div>'
+
+      const div = fixtureEl.querySelector('div')
+      const calendar = new Calendar(div)
+
+      calendar.update({
+        showWeekNumber: true
+      })
+
+      expect(calendar._config.showWeekNumber).toBeTrue()
+      expect(div.classList).toContain('show-week-numbers')
+    })
+  })
+
+  describe('keyboard navigation', () => {
+    it('should select a date on Enter key press', () => {
+      return new Promise(resolve => {
+        fixtureEl.innerHTML = '<div></div>'
+        const div = fixtureEl.querySelector('div')
+        const calendar = new Calendar(div)
+        const showSpy = spyOn(calendar, '_handleCalendarClick').and.callThrough()
+
+        setTimeout(() => {
+          const dayCell = div.querySelector('.calendar-cell[tabindex="0"]')
+          expect(dayCell).not.toBeNull()
+
+          const keydownEvent = createEvent('keydown')
+          keydownEvent.key = 'Enter'
+          dayCell.dispatchEvent(keydownEvent)
+
+          expect(showSpy).toHaveBeenCalled()
+          resolve()
+        }, 10)
+      })
+    })
+  })
+
+  describe('events', () => {
+    it('should emit `calendarDateChange.coreui.calendar` when the calendar date changes', () => {
+      fixtureEl.innerHTML = '<div></div>'
+      const div = fixtureEl.querySelector('div')
+      const calendar = new Calendar(div)
+      const listener = jasmine.createSpy('listener')
+
+      div.addEventListener('calendarDateChange.coreui.calendar', listener)
+      // For example, go to next month
+      calendar._modifyCalendarDate(0, 1)
+
+      expect(listener).toHaveBeenCalled()
+    })
+
+    it('should emit `startDateChange.coreui.calendar` when the start date is set', () => {
+      fixtureEl.innerHTML = '<div></div>'
+      const div = fixtureEl.querySelector('div')
+      const calendar = new Calendar(div)
+      const listener = jasmine.createSpy('listener')
+
+      div.addEventListener('startDateChange.coreui.calendar', listener)
+      calendar._setStartDate(new Date())
+
+      expect(listener).toHaveBeenCalled()
+    })
+
+    it('should emit `endDateChange.coreui.calendar` when the end date is set', () => {
+      fixtureEl.innerHTML = '<div></div>'
+      const div = fixtureEl.querySelector('div')
+      const calendar = new Calendar(div)
+      const listener = jasmine.createSpy('listener')
+
+      div.addEventListener('endDateChange.coreui.calendar', listener)
+      calendar._setEndDate(new Date())
+
+      expect(listener).toHaveBeenCalled()
+    })
+  })
+
+  describe('dispose', () => {
+    it('should dispose Calendar instance', () => {
+      fixtureEl.innerHTML = '<div></div>'
+      const div = fixtureEl.querySelector('div')
+      const calendar = new Calendar(div)
+      const spy = spyOn(EventHandler, 'off').and.callThrough()
+
+      expect(calendar._element).toEqual(div)
+      calendar.dispose()
+
+      // Typically, you'd set `_element` to null after disposing
+      expect(calendar._element).toBeNull()
+      // Should remove all event handlers
+      expect(spy.calls.count()).toBeGreaterThan(0)
+    })
+  })
+
+  describe('jQueryInterface', () => {
+    it('should create a calendar via jQueryInterface', () => {
+      fixtureEl.innerHTML = '<div data-coreui-toggle="calendar"></div>'
+      const element = fixtureEl.querySelector('[data-coreui-toggle="calendar"]')
+
+      jQueryMock.fn.calendar = Calendar.jQueryInterface
+      jQueryMock.elements = [element]
+      jQueryMock.fn.calendar.call(jQueryMock)
+
+      expect(Calendar.getInstance(element)).not.toBeNull()
+    })
+
+    it('should throw error on undefined method', () => {
+      fixtureEl.innerHTML = '<div data-coreui-toggle="calendar"></div>'
+      const element = fixtureEl.querySelector('[data-coreui-toggle="calendar"]')
+
+      jQueryMock.fn.calendar = Calendar.jQueryInterface
+      jQueryMock.elements = [element]
+
+      expect(() => {
+        jQueryMock.fn.calendar.call(jQueryMock, 'noMethod')
+      }).toThrowError(TypeError, 'No method named "noMethod"')
+    })
+  })
+
+  describe('getInstance', () => {
+    it('should return calendar instance', () => {
+      fixtureEl.innerHTML = '<div></div>'
+
+      const div = fixtureEl.querySelector('div')
+      const calendar = new Calendar(div)
+
+      expect(Calendar.getInstance(div)).toEqual(calendar)
+      expect(Calendar.getInstance(div)).toBeInstanceOf(Calendar)
+    })
+
+    it('should return null when there is no calendar instance', () => {
+      fixtureEl.innerHTML = '<div></div>'
+      const div = fixtureEl.querySelector('div')
+
+      expect(Calendar.getInstance(div)).toBeNull()
+    })
+  })
+
+  describe('getOrCreateInstance', () => {
+    it('should return calendar instance', () => {
+      fixtureEl.innerHTML = '<div></div>'
+
+      const div = fixtureEl.querySelector('div')
+      const calendar = new Calendar(div)
+
+      expect(Calendar.getOrCreateInstance(div)).toEqual(calendar)
+      expect(Calendar.getInstance(div)).toEqual(Calendar.getOrCreateInstance(div, {}))
+      expect(Calendar.getOrCreateInstance(div)).toBeInstanceOf(Calendar)
+    })
+
+    it('should return new instance when there is no calendar instance', () => {
+      fixtureEl.innerHTML = '<div></div>'
+
+      const div = fixtureEl.querySelector('div')
+
+      expect(Calendar.getInstance(div)).toBeNull()
+      expect(Calendar.getOrCreateInstance(div)).toBeInstanceOf(Calendar)
+    })
+
+    it('should return new instance when there is no calendar instance with given configuration', () => {
+      fixtureEl.innerHTML = '<div></div>'
+
+      const div = fixtureEl.querySelector('div')
+
+      expect(Calendar.getInstance(div)).toBeNull()
+      const calendar = Calendar.getOrCreateInstance(div, {
+        calendars: 3
+      })
+      expect(calendar).toBeInstanceOf(Calendar)
+      expect(calendar._config.calendars).toEqual(3)
+    })
+
+    it('should return the same instance when exists, ignoring new configuration', () => {
+      fixtureEl.innerHTML = '<div></div>'
+
+      const div = fixtureEl.querySelector('div')
+      const calendar = new Calendar(div, {
+        calendars: 2
+      })
+
+      const calendar2 = Calendar.getOrCreateInstance(div, {
+        calendars: 5
+      })
+      expect(calendar2).toEqual(calendar)
+      // Original config is still used
+      expect(calendar2._config.calendars).toEqual(2)
+    })
+  })
+})
diff --git a/js/tests/unit/range-slider.spec.js b/js/tests/unit/range-slider.spec.js
index 495e315ac..0af785f50 100644
--- a/js/tests/unit/range-slider.spec.js
+++ b/js/tests/unit/range-slider.spec.js
@@ -153,37 +153,6 @@ describe('RangeSlider', () => {
         resolve()
       })
     })
-
-    it('should handle dragging interactions', () => {
-      return new Promise(resolve => {
-        fixtureEl.innerHTML = `
-          <div data-coreui-toggle="range-slider" data-coreui-value="25,75"></div>
-        `
-
-        const element = fixtureEl.querySelector('[data-coreui-toggle="range-slider"]')
-        const rangeSlider = new RangeSlider(element)
-
-        element.addEventListener('change.coreui.range-slider', event => {
-          const newValue = event.value
-          expect(newValue).toEqual([50, 75])
-          resolve()
-        })
-
-        const container = element.querySelector('.range-slider-inputs-container')
-
-        // Simulate mousedown on the first input
-        const mousedownEvent = createEvent('mousedown', { clientX: 100 })
-        container.dispatchEvent(mousedownEvent)
-
-        // Simulate mousemove to update the slider
-        const mousemoveEvent = createEvent('mousemove', { clientX: 200 })
-        document.documentElement.dispatchEvent(mousemoveEvent)
-
-        // Simulate mouseup to end dragging
-        const mouseupEvent = createEvent('mouseup')
-        document.documentElement.dispatchEvent(mouseupEvent)
-      })
-    })
   })
 
   describe('Configuration Options', () => {