Create component testing for UsernameInput component

[MCatherine1994]

Describe the task
Since we separate the user name input form field into a new component in #1069, we can test it separately.

Acceptance Criteria

• test the username input, set the input with a value and verify the input is expected
• test the props, receive props correctly
• test the emit function
  • "change", when input change, the emit function is called
  • "setVerifyResult", when username verified, the emit function is called
• test enter in the input field will enable the verify button
• test the verify button shows "loading" while waiting for api result
• test the username verification
  • give a valid username, mock the api to return some user information (test the success case), check if user information card is displayed with expected information
  • give a not found username, mock the api to return not found response, check if user information card is displayed with expected "user does not exists" information
• test when props.domain change, user information card will be removed, setVerifyResult will be called with different parameter

Additional context

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