Check for duplicates in coded value domain

[LaimonasLiskauskas]

There is no check for duplicates in coded value domain during the creation of new codes and descriptions. The specified code value could already exists within the domain, but user has no information about this when he clicks on Ok or Apply button after typing the same value. The field representing the description of code value may also contain duplicate values. This problem is very actual in case user has large domains. Please add validation for code and description values.

[SSWoodward]

In ArcGIS Pro, users are prevented from creating new coded value pairs when the provided code is already present within the domain. 

For coded value descriptions, ArcGIS Pro does not enforce uniqueness. This is as designed.