Add and refactor tests for features of element select on a test-site

[annav00]

Add and refactor tests for features of element select on a test-site:

• [ ] append-icon (icon)
• [ ] append-outer-icon (y/n)
• [ ] autofocus (y/n)
• [ ] background-color (name of material color or css color)
• [ ] chips (y/n)
• [ ] clear-icon (icon)
• [ ] theme (dark/light)
• [ ] deletable-chips (y/n)
• [ ] dense (y/n)
• [ ] disable-lookup (y/n)
• [ ] error-count (number)
• [ ] filled (y/n)
• [ ] flat (y/n)
• [ ] full-width (y/n)
• [ ] height (0-n)
• [ ] hide-details (y/n)
• [ ] hide-selected (y/n)
• [ ] hide-spin-buttons (y/n)
• [ ] items (array)
• [ ] loader-height (0-n)
• [ ] loading (y/n)
• [ ] messages (string)
• [ ] no-data-text (string)
• [ ] open-on-clear (y/n)
• [ ] outlined (y/n)
• [ ] persistent-hint (y/n)
• [ ] persistent-placeholder (y/n)
• [ ] placeholder (string)
• [ ] prefix (y/n)
• [ ] prepend-inner-icon (icon)
• [ ] reverse (y/n)
• [ ] rounded (y/n)
• [ ] shaped (y/n)
• [ ] single-line (y/n)
• [ ] small-chips (y/n)
• [ ] solo (y/n)
• [ ] solo-inverted (y/n)
• [ ] suffix (y/n)
• [ ] validate-on-blur (y/n)