test: e2e test coverage for checking if content is loaded properly after opening again

[anon-pradip]

Description

Related Issue

• Test coverage for: [bug] Reopening the file doesn't load the slide content #13
• Part of: [Test] Add UI testing #16

Motivation and Context

How Has This Been Tested?

• test environment:
• test case 1:
• test case 2:

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Tests only (no source changes)
• Documentation only (no source changes)
• Maintenance (e.g. dependency updates or tooling)

Checklist:

• Code changes
• Unit tests added
• Acceptance tests added
• Documentation updated