Goto Marbles app.
Click on + icon to Create Marble.
Do not enter color and size
Click on create button.
An error is displayed .
So there should be a validation for creating a marble ,here are two options.
Disable create icon until user selects color and size.
When user clicks on create button display a validation message stating please select color and size of the marble.
Goto Marbles app. Click on + icon to Create Marble. Do not enter color and size Click on create button. An error is displayed . So there should be a validation for creating a marble ,here are two options.