test: restructure and enhance validation unit tests

[vursen]

Description

• Moved binder unit tests under the validation namespace.
• Added unit tests that ensure the component properly implements the HasValidation interface methods. That was previously covered by integration tests but only to some extent.

A continuation of #4350.

Part of vaadin/platform#3066

Covered components

• ComboBox
• MultiSelectComboBox
• CheckboxGroup
• RadioButtonGroup
• DatePicker
• TimePicker
• DateTimePicker
• Select

Type of change

• Internal

Checklist

• I have read the contribution guide: https://vaadin.com/docs/latest/contributing/overview
• I have added a description following the guideline.
• The issue is created in the corresponding repository and I have referenced it.
• I have added tests to ensure my change is effective and works as intended.
• New and existing tests are passing locally with my change.
• I have performed self-review and corrected misspellings.

[sissbruecker]

Extracting the logic definitely makes sense, however this specific pattern results in a lot of noise in Sonar validation, because it does not detect the assertions:
https://sonarcloud.io/project/issues?resolved=false&types=CODE_SMELL&pullRequest=4356&id=vaadin_flow-components&open=AYUQ_8ljB57jh_TraguY

Could we use an abstract test class instead, like AbstractionBasicValidationTest was used in the text field module?

[vursen]

note: I assumed that this class can be removed likewise since it is no longer used in the codebase.

[sonarcloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
22 Code Smells

No Coverage information
0.0% Duplication