Oracle error ORA-12154

Good day, dear forumchane.

There was a question about working with the Oracle Database from Visual Studio 2013 (C#). When trying to connect to the database, Oracle returns the following error:

ORA-12154: TNS:could not resolve the connect identifier specified

Here is the connection code:

using System.Web.Mvc;
using Oracle.ManagedDataAccess.Client;


string oradb = "Data Source=WorkTest;User Id=C##;Password=123;";
            OracleConnection conn = new OracleConnection(oradb);  // C#
            conn.Open();
            OracleCommand cmd = new OracleCommand();
            cmd.Connection = conn;
            cmd.CommandText = "select * from ааа";
            cmd.CommandType = CommandType.Text;
            OracleDataReader dr = cmd.ExecuteReader();
            dr.Read();
            var cc = dr.GetString(0);
            conn.Dispose();

The error is thrown at the stage: conn.Open();.
According to the search results, it seems that the reason may be in the file tnsnames.ora. The file tnsnames.ora contains next:

# tnsnames.ora Network Configuration File: D:\app\username\product\12.1.0\dbhome_1\network\admin\tnsnames.ora
# Generated by Oracle configuration tools.

LISTENER_WORKTEST =
  (ADDRESS = (PROTOCOL = TCP)(HOST = localhost)(PORT = 1521))


ORACLR_CONNECTION_DATA =
  (DESCRIPTION =
    (ADDRESS_LIST =
      (ADDRESS = (PROTOCOL = IPC)(KEY = EXTPROC1521))
    )
    (CONNECT_DATA =
      (SID = CLRExtProc)
      (PRESENTATION = RO)
    )
  )

LISTENER_ORCL =
  (ADDRESS = (PROTOCOL = TCP)(HOST = localhost)(PORT = 1521))


WORKTEST =
  (DESCRIPTION =
    (ADDRESS = (PROTOCOL = TCP)(HOST = localhost)(PORT = 1521))
    (CONNECT_DATA =
      (SERVER = DEDICATED)
      (SERVICE_NAME = WorkTest)
    )
  )

ORCL =
  (DESCRIPTION =
    (ADDRESS = (PROTOCOL = TCP)(HOST = localhost)(PORT = 1521))
    (CONNECT_DATA =
      (SERVER = DEDICATED)
      (SERVICE_NAME = orcl)
    )
  )

Tell me what and where to look... I've been hanging out for two days now. ((
(I haven't worked with Oracl until now:()

Here:

Does the server have such a sid WorkTest? Here:

Here is created with TNS, all prikonektilos:

Here is still tried through SQL PLUS prikonektitsya, like all broke a, but why something not pass team SQL, although and must:

Update

Yes, the thing is that I don't even know how to check half of the parameters: (

File sqlnet.ora contains

# sqlnet.ora Network Configuration File: D:\app\username\product\12.1.0\dbhome_1\network\admin\sqlnet.ora
# Generated by Oracle configuration tools.

# This file is actually generated by netca. But if customers choose to 
# install "Software Only", this file wont exist and without the native 
# authentication, they will not be able to connect to the database on NT.

SQLNET.AUTHENTICATION_SERVICES= (NTS)

NAMES.DIRECTORY_PATH= (TNSNAMES, EZCONNECT)

Everything seems to be everywhere, but I don't know what to do(

And here is the solution to the problem:

I have already tried everything that is possible), yesterday I sat half the night. Here is who will be interested in the method of checking for this error in SQL Plus: https://www.youtube.com/watch?v=QVJ1xO2V7Dc. I followed it, and everything is fine. me, but through VS 2013 still brings down the error. But the reason, as always, was banal to the point of outrage:(, you must specify Data Source=localhost: 1521/WorkTest in the connection string instead of Data Source=WorkTest... and that's it!!!!... now only emotions:(.. and on the official site it is indicated that it is necessary to Data Source=WorkTest ... oh, thank you so much to everyone who helped). The issue is resolved, the project has passed)