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

[annav00]

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

• [x] append-icon (y/n)
• [x] background-color (name of material color or css color)
• [x] color (name of material color or css color)
• [x] theme (dark/light)
• [x] dense (y/n)
• [x] error (y/n)
• [x] error-count (0-n)
• [x] error-messages (string)
• [x] flat (y/n)
• [x] hide-details (y/n)
• [x] hint (string) - message
• [x] inset (y/n)
• [x] messages (sting)
• [x] persistent-hint (y/n) message
• [x] prepend-icon (y/n)
• [x] readonly (y/n)
• [x] ripple (y/n)
• [x] success (y/n)
• [x] success-messages (string)
• [x] value (value)