How to use .NET User Secrets in MSTest classes

When developing unit and integration tests, we don't necessarily want to share the secret keys and values we use as credentials for APIs, databases, etc.

So similarly to how we implement User Secret functionality in Program.cs, we can implement User Secrets and set test class variables that use the secrets via the MSTest classes' constructor (ReferenceDataTests() below):

  public static string upsId = "";  
  public static string upsSecret = "";  
  private IConfiguration _configuration { get; }  
  
  public ReferenceDataTests()  
  {  
    // set your API ids and secrets in UserSecrets (right-click project: "Manage User Secrets")  
    var builder = new ConfigurationBuilder()  
      .AddUserSecrets<ReferenceDataTests>();  
    _configuration = builder.Build(); 
    
    var secretVals = _configuration.GetChildren().ToList();  
    upsId = secretVals.Where(x => x.Key == "upsId").First().Value!;  
    upsSecret = secretVals.Where(x => x.Key == "upsSecret").First().Value!;   
  }  

Reference: https://stackoverflow.com/questions/41941503/how-to-use-user-secrets-in-a-dotnet-core-test-project