[scheduler] Testing - event builders for reducing test boilerplate

[rita-codes]

A tiny, type-safe Event Builder for tests with a simple API for complex things like recurrence

Why this helps

• Slashes boilerplate in tests.
  Tests no longer need to manually create full CalendarEvent objects with adapter.date(...) everywhere.
  Common patterns like "single-day timed event", "all-day span", or "weekly recurrence" become one-liners, which keeps tests readable and focused on behavior instead of setup.
• Consistent with production logic.
  The builder relies on the adapter so it automatically respects locale, time zones, and weekday mapping, no more mismatches caused by hardcoded weekday codes or date math.
• Safer defaults: if you don't need to use the title, or another property, they're automatically filled with sensible defaults (reducing boilerplate even further)

Use examples
Full default event:
Produces a valid CalendarEventOccurrence with: Randomized id, auto title and description, starts at DEFAULT_TESTING_VISIBLE_DATE, duration 60 min and realistic key.

const event = EventBuilder.new().build();

Weekly recurring event with startAt

const event = EventBuilder.new()
.singleDay('2025-07-02T09:00:00Z', 30)
.recurrent('weekly')
.build();

All day spaning multiple days with title

const event = EventBuilder.new()
  .title('Conference')
  .span('2025-07-10T09:00:00Z', '2025-07-12T18:00:00Z', { allDay: true })
  .build();

• I have followed (at least) the PR section of the contributing guide.

[mui-bot]

Deploy preview: https://deploy-preview-20081--material-ui-x.netlify.app/

Bundle size report

Bundle	Parsed size	Gzip size
@mui/x-data-grid	0B(0.00%)	0B(0.00%)
@mui/x-data-grid-pro	0B(0.00%)	0B(0.00%)
@mui/x-data-grid-premium	0B(0.00%)	0B(0.00%)
@mui/x-charts	0B(0.00%)	0B(0.00%)
@mui/x-charts-pro	0B(0.00%)	0B(0.00%)
@mui/x-charts-premium	0B(0.00%)	0B(0.00%)
@mui/x-date-pickers	0B(0.00%)	0B(0.00%)
@mui/x-date-pickers-pro	0B(0.00%)	0B(0.00%)
@mui/x-tree-view	0B(0.00%)	0B(0.00%)
@mui/x-tree-view-pro	0B(0.00%)	0B(0.00%)

Details of bundle changes

Generated by 🚫 dangerJS against 617c345

[flaviendelangle]

One final comment and we are good to go.

Thanks for doing it!
It will make the tests a lot more robust and easy to manipulate!