test(datetime-button): add tests for datetime constraints

- should default to exact current time with no constraints
- should obey minuteValues constraint
- should obey hourValues constraint
- should obey monthValues constraint

Author: droc101

core/src/components/datetime-button/test/basic/datetime-button.e2e.ts

@@ -344,4 +344,154 @@ configs({ modes: ['md'], directions: ['ltr'] }).forEach(({ title, config }) => {
       await expect(page.locator('ion-datetime-button')).toContainText('Thu, November 02 01:22 AM');
     });
   });
+
+  test.describe(title('datetime-button: datetime constraints'), () => {
+    test('should default to exact current time with no constraints', async ({ page }) => {
+      const fixedTime = new Date('2026-06-18T17:54:54.518Z');
+      await page.clock.setFixedTime(fixedTime);
+
+      await page.setContent(
+        `
+        <ion-datetime-button datetime="datetime"></ion-datetime-button>
+        <ion-datetime id="datetime" presentation="date-time" locale="en-US"></ion-datetime>
+        <script>
+          const datetime = document.querySelector('ion-datetime');
+          datetime.formatOptions = {
+            date: {
+              weekday: "short",
+              month: "long",
+              day: "2-digit"
+            },
+            time: {
+              hour: "2-digit",
+              minute: "2-digit"
+            }
+          }
+        </script>
+      `,
+        config
+      );
+      await page.locator('.datetime-ready').waitFor();
+
+      const dateFormat = new Intl.DateTimeFormat('en-US', {
+        weekday: 'short',
+        month: 'long',
+        day: '2-digit',
+      });
+      const timeFormat = new Intl.DateTimeFormat('en-US', {
+        hour: '2-digit',
+        minute: '2-digit',
+      });
+
+      await expect(page.locator('#date-button')).toContainText(dateFormat.format(fixedTime));
+      await expect(page.locator('#time-button')).toContainText(timeFormat.format(fixedTime));
+    });
+
+    test('should obey minuteValues constraint', async ({ page }) => {
+      const fixedTime = new Date('2026-06-18T17:54:54.518Z');
+      await page.clock.setFixedTime(fixedTime);
+
+      await page.setContent(
+        `
+        <ion-datetime-button datetime="datetime"></ion-datetime-button>
+        <ion-datetime id="datetime" presentation="time" locale="en-US" minute-values="0"></ion-datetime>
+        <script>
+          const datetime = document.querySelector('ion-datetime');
+          datetime.formatOptions = {
+            time: {
+              hour: "2-digit",
+              minute: "2-digit"
+            }
+          }
+        </script>
+      `,
+        config
+      );
+      await page.locator('.datetime-ready').waitFor();
+
+      await page.pause();
+
+      const expectedTime = fixedTime;
+      expectedTime.setMinutes(0);
+
+      const timeFormat = new Intl.DateTimeFormat('en-US', {
+        hour: '2-digit',
+        minute: '2-digit',
+      });
+
+      await expect(page.locator('#time-button')).toContainText(timeFormat.format(expectedTime));
+    });
+
+    test('should obey hourValues constraint', async ({ page }) => {
+      const fixedTime = new Date('2026-06-18T17:54:54.518Z');
+      await page.clock.setFixedTime(fixedTime);
+
+      await page.setContent(
+        `
+        <ion-datetime-button datetime="datetime"></ion-datetime-button>
+        <ion-datetime id="datetime" presentation="time" locale="en-US" hour-values="0"></ion-datetime>
+        <script>
+          const datetime = document.querySelector('ion-datetime');
+          datetime.formatOptions = {
+            time: {
+              hour: "2-digit",
+              minute: "2-digit"
+            }
+          }
+        </script>
+      `,
+        config
+      );
+      await page.locator('.datetime-ready').waitFor();
+
+      await page.pause();
+
+      const expectedTime = fixedTime;
+      expectedTime.setHours(0);
+
+      const timeFormat = new Intl.DateTimeFormat('en-US', {
+        hour: '2-digit',
+        minute: '2-digit',
+      });
+
+      await expect(page.locator('#time-button')).toContainText(timeFormat.format(expectedTime));
+    });
+
+    test('should obey monthValues constraint', async ({ page }) => {
+      const fixedTime = new Date('2026-06-18T17:54:54.518Z');
+      await page.clock.setFixedTime(fixedTime);
+
+      await page.setContent(
+        `
+        <ion-datetime-button datetime="datetime"></ion-datetime-button>
+        <ion-datetime id="datetime" presentation="date" locale="en-US" month-values="1"></ion-datetime>
+        <script>
+          const datetime = document.querySelector('ion-datetime');
+          datetime.formatOptions = {
+            date: {
+              weekday: "short",
+              month: "long",
+              day: "2-digit"
+            }
+          }
+        </script>
+      `,
+        config
+      );
+      await page.locator('.datetime-ready').waitFor();
+
+      await page.pause();
+
+      const expectedTime = fixedTime;
+      expectedTime.setMonth(0);
+
+      const dateFormat = new Intl.DateTimeFormat('en-US', {
+        weekday: 'short',
+        month: 'long',
+        day: '2-digit',
+      });
+
+      await expect(page.locator('#date-button')).toContainText(dateFormat.format(expectedTime));
+    });
+  });
 });